Meow's GeneralNote - Screws 螺丝
Screws 螺丝
Overview 概述
螺丝是最常见的紧固件 (Fastener)：靠螺纹把旋转的力变成夹紧的力，把两个零件压在一起。眼镜、手机、电脑、家具、房屋、汽车里都有螺丝。本文从零开始介绍：螺丝由哪些部分组成、常见种类、起子头类型、怎么读规格、怎么选长度和粗细、预钻孔和沉头孔，以及垫圈、螺母、预埋螺母这些配件。
A screw is the most common fastener: its thread turns rotation into clamping force that presses two parts together. Screws hold together glasses, phones, computers, furniture, houses and cars. This note starts from zero: the parts of a screw, the common types, drive types, how to read a size label, how to pick length and diameter, pilot holes and countersinks, and accessories such as washers, nuts and inserts.
1. Anatomy of a Screw 螺丝的结构
| 部位 Part | 说明 | Description |
|---|---|---|
| 头部 Head | 螺丝最上面较宽的部分，挡住螺丝不让它穿过去 | The wide top that stops the screw from passing through |
| 驱动槽 Drive | 头部上用来插起子的凹槽（十字、梅花等） | The recess in the head that the driver bit fits into |
| 光杆 Shank | 头部下面没有螺纹的光滑部分（部分螺丝没有） | The smooth, unthreaded section under the head (not on every screw) |
| 螺纹 Thread | 绕着螺杆的螺旋棱，负责”咬住”材料 | The spiral ridge that grips the material |
| 外径 Major diameter | 螺纹最外侧的直径，即”规格”里的粗细 | Diameter measured across the thread tips; this is the size on the label |
| 底径 Minor / root diameter | 螺纹根部（芯）的直径，决定预钻孔大小 | Diameter of the solid core; this sets the pilot hole size |
| 螺距 Pitch | 相邻两圈螺纹之间的距离 | Distance between neighboring thread crests |
| 尖端 Point | 尖头（自攻）或平头（机械螺丝） | Sharp tip (self-tapping) or flat end (machine screw) |
Screw vs Bolt 螺丝 vs 螺栓
- 螺丝 Screw：通常直接拧进材料，靠材料本身或预制的螺纹固定。/ Usually driven straight into the material, gripping it directly or a pre-made thread.
- 螺栓 Bolt：穿过两个零件上的通孔，另一端用螺母拧紧夹住。/ Passes through clearance holes in both parts and is clamped by a nut on the far side.
日常说话里这两个词经常混用，买东西时看清楚是否需要配螺母即可。
In everyday speech the two words are often mixed up. When buying, what matters is whether a nut is needed.
Head Types 头部形状
| 头型 Head | 样子 | Look | 用途 Use |
|---|---|---|---|
| 沉头 Flat / Countersunk | 锥形，拧完与表面平齐 | Cone-shaped, sits flush with the surface | 木工、铰链、需要表面平整处 / Woodworking, hinges, flush surfaces |
| 盘头 Pan | 圆顶略扁，凸在表面上 | Low dome that stays above the surface | 电子、金属片、塑料件 / Electronics, sheet metal, plastic |
| 喇叭头 Bugle | 弧形过渡的沉头 | Countersunk with a curved underside | 石膏板 / Drywall |
| 垫圈头 Washer / Flange | 头部自带一圈宽边 | Head with a built-in wide flange | 斜孔螺丝、薄板 / Pocket holes, thin panels |
| 六角头 Hex | 六角形，用扳手拧 | Hexagonal, turned with a wrench | 重型结构、螺栓 / Heavy structures, bolts |
2. Screw Types 螺丝种类
2.1 Machine Screw vs Self-Tapping Screw 机械螺丝 vs 自攻螺丝
这是新手最需要先分清的一点。
This is the first distinction a beginner needs.
| 机械螺丝 Machine Screw | 自攻螺丝 Self-Tapping Screw | |
|---|---|---|
| 螺纹 Thread | 细而均匀，平头 / Fine, even, blunt end | 粗而深，通常尖头 / Coarse, deep, usually pointed |
| 拧进哪里 Goes into | 螺母、预埋螺母、攻好丝的金属孔 / A nut, an insert, or a tapped metal hole | 直接拧进木头、塑料、薄金属 / Straight into wood, plastic or thin metal |
| 规格写法 Label | M3 x 10, M4 x 20 | ST3.5 x 16, #8 x 1-1/4” |
| 能否反复拆装 Reusable | 可以，螺纹不磨损 / Yes, the thread does not wear | 次数有限，木头/塑料螺纹会磨坏 / Limited; the wood/plastic thread wears out |
说明书写 “M3” 一般指机械螺丝，需要配螺母或预埋螺母。如果是 3D 打印件或木工结合件，通常需要配合螺母或热熔预埋螺母使用。
When a manual says “M3”, it usually means a machine screw that needs a nut or an insert. For 3D-printed parts or wood joints, it is typically paired with a nut or a heat-set insert.
2.2 Wood Screw 木螺丝
- 粗螺纹、尖头，专门咬住木纤维。/ Coarse thread and sharp point made to grip wood fibers.
- 传统木螺丝上半段是光杆（部分螺纹）。光杆在上面那块板里自由转动，螺纹只咬下面那块，于是能把两块板拉紧贴合。/ Traditional wood screws are partially threaded. The smooth shank turns freely in the top board while the thread bites only the bottom board, which pulls the two boards tight.
- 全螺纹的螺丝会同时咬住两块板，板之间容易留缝（”顶起”）。/ A fully threaded screw grips both boards at once and can leave a gap between them (“jacking”).
- 户外用镀锌或不锈钢；防腐处理木 (ACQ) 腐蚀性强，要用热镀锌或不锈钢螺丝。/ Outdoors, use galvanized or stainless steel. Pressure-treated (ACQ) lumber is corrosive and needs hot-dip galvanized or stainless screws.
2.3 Drywall Screw 石膏板螺丝
- 黑色磷化涂层，喇叭头，用来把石膏板固定在龙骨上。/ Black phosphate coating and bugle head, made to hold drywall to studs.
- 喇叭头能压住石膏板表面的纸而不撕破。/ The bugle head presses the paper face without tearing it.
- 粗牙用于木龙骨，细牙用于轻钢龙骨。/ Coarse thread for wood studs, fine thread for metal studs.
- 不要用于家具或承重结构
：钢材很硬但很脆，受侧向力时会直接断掉，而不是弯曲。因为便宜常被误用。/ Do not use for furniture or load-bearing work: the steel is hard but brittle and snaps under sideways load instead of bending. It gets misused because it is cheap.
2.4 Pocket-Hole Screw 斜孔螺丝
- 配合斜孔夹具 (Pocket-hole jig，如 Kreg) 使用：在一块板上以约 15 度斜角钻孔，螺丝斜着拧进另一块板，常用于桌面框架、柜体框。/ Used with a pocket-hole jig (such as Kreg): a hole is drilled at about 15 degrees in one board, and the screw is driven at that angle into the other board. Common in face frames and table aprons.
- 垫圈头：平底头压在斜孔底部，不会把孔撑裂。/ Washer head: the flat underside sits on the bottom of the pocket without splitting it.
- 自攻尖：尖端带切口，不需要在第二块板上预钻孔。/ Self-drilling tip: a cutting notch at the point means no pilot hole is needed in the second board.
- 粗牙用于软木和夹板，细牙用于硬木。/ Coarse thread for softwood and plywood, fine thread for hardwood.
| 板厚 Board thickness | 螺丝长度 Screw length |
|---|---|
| 1/2” (12 mm) | 3/4” (19 mm) |
| 3/4” (19 mm) | 1-1/4” (32 mm) |
| 1-1/2” (38 mm) | 2-1/2” (64 mm) |
2.5 Confirmat Screw 家具专用 Confirmat 螺丝（三合一连接螺丝）
- 一体式家具连接螺丝，专门用于刨花板、密度板 (MDF) 等板式家具。/ A one-piece furniture connector made for particleboard and MDF panel furniture.
- 很粗（常见 7 x 50 mm）、螺纹深且宽，能咬住松散的板材芯。/ Thick (7 x 50 mm is common) with a deep, wide thread that grips the loose core of panel material.
- 需要专用阶梯钻头：一次钻出底孔、光杆孔和沉头孔。/ Needs a special stepped drill bit that cuts the pilot hole, shank hole and countersink in one pass.
- 常用 4 mm 内六角或米字起子拧。/ Usually driven with a 4 mm hex key or a Pozidriv bit.
- 宜家常见的另一种是偏心件 (Cam lock)：圆形偏心轮 + 连接杆，转半圈就锁紧，方便拆装但强度低于 Confirmat。/ The other common IKEA connector is the cam lock: a round cam plus a connecting bolt that locks with a half turn. It is easier to take apart but weaker than a Confirmat.
3. Drive Types 起子头类型
驱动槽决定用哪种起子头。起子头和槽不匹配是”螺丝头被拧花 (Stripped / Cam-out)”的头号原因。
The drive recess decides which bit to use. A mismatched bit is the number one cause of stripped screw heads (cam-out).
| 类型 Type | 中文俗称 | 标记 Code | 常见尺寸 Common sizes | 特点 Notes |
|---|---|---|---|---|
| Phillips | 十字 | PH | PH1, PH2（最常见 / most common）, PH3 | 设计上力大时会”跳出”，容易拧花 / Designed to cam out under high torque, strips easily |
| Pozidriv | 米字 | PZ | PZ1, PZ2, PZ3 | 十字之间多四条细线，咬合更紧；欧洲和宜家常用 / Four extra tick marks between the arms, grips tighter; common in Europe and IKEA |
| Torx | 梅花（六角星） | T | T10, T20, T25 | 六瓣星形，几乎不打滑，适合大扭矩、户外和甲板螺丝 / Six-lobed star that barely slips; good for high torque, outdoor and deck screws |
| Square / Robertson | 方头 | R / SQ | #1 绿 green, #2 红 red, #3 黑 black | 方形孔，螺丝能”挂”在起子头上不掉，加拿大和北美木工常用 / Square recess that holds the screw on the bit; popular in Canada and North American woodworking |
| Slotted | 一字 | SL | 按刀口宽度 / by blade width | 最古老，最容易滑，多见于老家具和电源插座 / Oldest and slips the most; seen on old furniture and outlets |
| Hex socket | 内六角 | H / mm | 2, 2.5, 3, 4, 5 mm | 用内六角扳手（Allen key），机械螺丝和板式家具常用 / Turned with an Allen key; common on machine screws and flat-pack furniture |
Phillips vs Pozidriv 十字 vs 米字
米字槽从远处看像十字，但在四个角之间多了四条细刻线。用十字起子拧米字螺丝能转，但只接触一部分，很容易拧花。拧之前先看清楚有没有那四条细线。
A Pozidriv recess looks like Phillips from a distance, but it has four thin tick marks between the arms. A Phillips bit will turn a Pozidriv screw but only touches part of the recess and strips it easily. Check for the tick marks before driving.
4. Reading Sizes 怎么读规格
4.1 Metric 公制
M4 x 20 的意思：
M4 x 20 means:
- M = 公制粗牙螺纹 / Metric coarse thread
- 4 = 螺纹外径 4 mm / Major diameter 4 mm
- 20 = 长度 20 mm / Length 20 mm
- 细牙会额外标螺距，如
M8 x 1.0 x 30；不标就是标准粗牙。/ Fine thread adds the pitch, e.g.M8 x 1.0 x 30; no pitch means standard coarse.
：沉头螺丝从头顶量到尖端（整颗长度）；盘头、六角头等从头部下面量到尖端（头部不算）。
How length is measured: countersunk screws are measured from the top of the head to the tip (full length); pan, hex and other raised heads are measured from under the head to the tip (head excluded).
4.2 Imperial 英制
- 木螺丝：
#8 x 1-1/4"= 8 号粗细（约 4.2 mm），长 1.25 英寸。号数越大越粗：#6 约 3.5 mm，#8 约 4.2 mm，#10 约 4.8 mm。/ Wood screws:#8 x 1-1/4"= gauge 8 (about 4.2 mm), 1.25 inches long. Higher gauge is thicker: #6 is about 3.5 mm, #8 about 4.2 mm, #10 about 4.8 mm. - 机械螺丝/螺栓：
1/4"-20 x 1"= 直径 1/4 英寸，每英寸 20 圈螺纹，长 1 英寸。相机三脚架接口就是 1/4”-20。/ Machine screws and bolts:1/4"-20 x 1"= 1/4 inch diameter, 20 threads per inch, 1 inch long. Camera tripod mounts use 1/4”-20. - 英制和公制不能混用：M6 和 1/4” 粗细接近但螺纹不同，硬拧会毁掉螺纹。/ Imperial and metric do not mix: M6 and 1/4” are close in size but have different threads, and forcing one into the other ruins the thread.
5. Common Metric (M-Series) Sizes and Uses 常用公制螺丝（M 系列）规格与应用场景
公制螺丝从很细的微型螺丝到建筑重型螺栓都有。下表整理了木工、DIY 及日常生活中最常见的 M 规格。
Metric screws range from tiny micro screws to heavy construction bolts. The table below lists the M sizes most common in woodworking, DIY and daily life.
| 螺丝规格 Size | 螺杆外径 Diameter | 粗牙螺距 Coarse pitch | 典型应用场景 | Typical uses |
|---|---|---|---|---|
| M1.4 - M2 | 1.4 - 2.0 mm | 0.3 - 0.4 mm | 精密电子与模型：眼镜框、手机、手表、小型航模、微型无刷电机 | Precision electronics and models: glasses frames, phones, watches, small RC aircraft, micro brushless motors |
| M2.5 - M3 | 2.5 - 3.0 mm | 0.45 - 0.5 mm | 小型 DIY 与 3D 打印：3D 打印零件组装、小型木盒铰链、树莓派/电脑主板固定、轻量手工作品 | Small DIY and 3D printing: printed part assembly, small wooden box hinges, Raspberry Pi and motherboard mounting, light crafts |
| M4 - M5 | 4.0 - 5.0 mm | 0.7 - 0.8 mm | 轻型家具与设备：电脑桌配件、柜门拉手/把手、3D 打印机结构件、小型滑轨固定 | Light furniture and equipment: desk accessories, cabinet door handles, 3D printer frames, small drawer slides |
| M6 - M8 | 6.0 - 8.0 mm | 1.0 - 1.25 mm | 中型木工与家具：宜家板式家具组装、办公桌腿固定、木工夹具、床架与支撑结构 | Medium woodworking and furniture: IKEA flat-pack assembly, desk legs, woodworking jigs, bed frames and supports |
| M10 - M12 | 10.0 - 12.0 mm | 1.5 - 1.75 mm | 重型结构：重型木桌脚、户外木结构（如凉亭/围栏）、重机械与金属框架固定 | Heavy structures: heavy table legs, outdoor wood structures such as gazebos and fences, heavy machinery and metal frames |
6. Choosing Length and Diameter 尺寸和长度怎么选
6.1 Length 长度
木头对木头时的经验法则：
Rules of thumb for wood-to-wood joints:
- 螺纹至少要拧进下面那块板 2/3 的厚度，咬得越深越牢。/ The thread should go at least two-thirds of the way into the bottom board; deeper bite means a stronger hold.
- 尖端离下面那块板的背面至少留 3 mm (1/8”)，避免穿出来。/ Leave at least 3 mm (1/8”) between the tip and the back face of the bottom board so it does not poke through.
- 简单算法：长度 ≈ 上板厚度 + 下板厚度的 2/3 左右。/ Quick formula: length ≈ top board thickness + about two-thirds of the bottom board thickness.
- 例：两块 18 mm 的板叠在一起，选 30 - 32 mm 左右。/ Example: two 18 mm boards stacked, pick about 30 - 32 mm.
机械螺丝配螺母时：长度 = 所有零件总厚度 + 垫圈 + 螺母厚度，再多出 1 - 2 圈螺纹。
For a machine screw with a nut: length = total thickness of all parts + washers + nut, plus 1 - 2 extra threads showing.
6.2 Diameter 粗细
- 越粗越牢，但也越容易把薄板或板边撑裂。/ Thicker is stronger but more likely to split thin boards and edges.
- 通用木工：#8 或 4 mm 是最万能的选择。/ General woodworking: #8 or 4 mm is the most versatile choice.
- 薄板、小五金（铰链、小把手）：#6 或 3 - 3.5 mm。/ Thin stock and small hardware (hinges, small pulls): #6 or 3 - 3.5 mm.
- 承重、户外：#10 以上或 5 mm 以上，更重的用方头螺栓 (Lag screw)。/ Load-bearing and outdoor: #10 or 5 mm and up; heavier jobs use lag screws.
- 买五金件（铰链、滑轨）时，优先用包装里附带的螺丝或说明书指定的规格，孔位是按它设计的。/ For hardware like hinges and slides, use the screws that come in the box or the size the manual specifies; the holes are designed for them.
7. Pilot Holes and Countersinks 预钻孔和沉头孔
7.1 Three Kinds of Holes 三种孔
| 孔 Hole | 打在哪里 Where | 大小 Size | 目的 Purpose |
|---|---|---|---|
| 预钻孔 Pilot hole | 下面那块板 / Bottom board | ≈ 螺丝底径 / ≈ minor diameter | 给螺纹留路，防止木头裂开 / Clears a path for the thread and stops splitting |
| 过孔 Clearance hole | 上面那块板 / Top board | ≈ 螺丝外径或略大 / ≈ major diameter or slightly larger | 螺丝在上板里自由转动，才能把两块板拉紧 / Lets the screw spin freely in the top board so it can pull the boards together |
| 沉头孔 Countersink | 上板表面 / Top board surface | 锥形，配合沉头螺丝 / Cone that matches a flat head | 让螺丝头与表面平齐 / Lets the head sit flush |
7.2 When a Pilot Hole Is Needed 什么时候要预钻孔
- 硬木（橡木、枫木、胡桃木）：一定要，否则螺丝可能拧断或木头开裂。/ Hardwood (oak, maple, walnut): always, or the screw may snap or the wood may split.
- 靠近板边或板端（端面木纹最容易裂）：一定要。/ Near an edge or end grain (end grain splits most easily): always.
- 软木（松木、杉木）用小螺丝：可以不打，但打了更整齐。/ Softwood (pine, fir) with small screws: optional, but neater with one.
- 刨花板、密度板：要，而且孔要打准，板材芯很松，拧歪就废了。/ Particleboard and MDF: yes, and accurately; the core is loose and a crooked screw ruins the hole.
- 硬木预钻孔接近底径，软木可以再小一点。/ In hardwood, match the pilot to the minor diameter; in softwood, go a little smaller.
| 螺丝 Screw | 软木预钻孔 Softwood pilot | 硬木预钻孔 Hardwood pilot | 过孔 Clearance |
|---|---|---|---|
| #6 / 3.5 mm | 2 mm (5/64”) | 2.5 mm (3/32”) | 3.5 - 4 mm (9/64”) |
| #8 / 4 mm | 2.5 mm (3/32”) | 3 mm (1/8”) | 4.5 mm (11/64”) |
| #10 / 5 mm | 3 mm (7/64”) | 3.5 mm (9/64”) | 5 mm (3/16”) |
7.3 Countersink vs Counterbore 沉头孔 vs 埋头孔
- 沉头孔 Countersink：锥形斜面，让沉头螺丝的锥形头刚好陷进去、与表面齐平。公制螺丝的锥角是 90 度，英制是 82 度。/ A cone-shaped recess that lets a flat head sit flush. Metric heads use a 90-degree angle, imperial heads 82 degrees.
- 埋头孔 Counterbore：平底圆孔，把整个螺丝头藏到表面以下，上面可以用木塞 (Wood plug) 盖住。/ A flat-bottomed round hole that hides the whole head below the surface, which can then be covered with a wood plug.
- 常用工具：带沉头的组合钻头 (Countersink drill bit)，一次钻出预钻孔 + 沉头孔。/ Common tool: a combination countersink bit that drills the pilot hole and the countersink in one pass.
7.4 Tapping Metal 金属攻丝底孔
在金属上攻螺纹给机械螺丝用时，底孔 ≈ 外径 - 螺距：
To tap a thread in metal for a machine screw, the tap drill ≈ major diameter - pitch:
| 规格 Size | 攻丝底孔 Tap drill | 过孔 Clearance hole |
|---|---|---|
| M3 | 2.5 mm | 3.2 - 3.4 mm |
| M4 | 3.3 mm | 4.3 - 4.5 mm |
| M5 | 4.2 mm | 5.3 - 5.5 mm |
| M6 | 5.0 mm | 6.4 - 6.6 mm |
| M8 | 6.8 mm | 8.4 - 9.0 mm |
8. Screw Accessories 螺丝配件
8.1 Flat Washer 平垫圈（小铁片）
长相：一个扁平的金属圆环片。
Look: a flat metal ring.
作用与原理 How it works:
- 增大接触面积：螺丝头很小，如果直接拧在木头或塑料上，容易把木头压凹陷。平垫圈能把压力均匀分散出去。/ Spreads the load: a screw head is small, and driven straight onto wood or plastic it can crush a dent. The washer spreads the pressure over a wider area.
- 保护表面：拧紧时螺丝头摩擦的是垫圈，而不会刮伤木材表面。/ Protects the surface: while tightening, the head rubs against the washer instead of scratching the wood.
用在哪里 Where: 软木、薄板、3D 打印件，或者孔开得稍微偏大的时候。/ Softwood, thin panels, 3D-printed parts, or a hole drilled slightly too large.
8.2 Lock Washer / Spring Washer 弹簧垫圈（小铁环）
长相：一个带缺口的圆环，缺口两端一高一低，像一个小弹簧。
Look: a split ring whose two ends are offset, like a tiny spring.
作用与原理 How it works:
- 防松动（抗震）：拧紧后被压平的弹簧持续提供弹力，缺口处的硬边会”咬住”螺丝头和接触面。在有震动（电机、滑轮、抽屉频繁拉合）时，能减缓螺丝自己慢慢松脱。/ Resists loosening from vibration: once flattened, the spring keeps pushing back, and the sharp edges at the split dig into the head and the surface. Under vibration (motors, pulleys, drawers opened often) this slows the screw from backing out on its own.
- 对强烈震动的场合，尼龙防松螺母 (Nyloc nut) 或螺纹胶 (Threadlocker) 通常更可靠。/ For heavy vibration, a nylon-insert lock nut (Nyloc) or threadlocker is usually more reliable.
用在哪里 Where: 有震动或频繁移动的家具、工具、滑轨固定处。/ Furniture, tools and slide mounts that vibrate or move often.
叠放顺序 Stacking order: 螺丝头 -> 弹簧垫圈 -> 平垫圈 -> 木头/物体。/ Screw head -> lock washer -> flat washer -> wood or part.
8.3 Nut 螺母（六角小块）
长相：外圈通常是六角形、中间带螺纹的金属件。
Look: a metal piece, usually hexagonal outside with a thread inside.
作用与原理 How it works: 与机械螺丝配套使用。螺丝穿过两块板材后，在另一端拧上螺母，形成”夹心饼干”式的强力固定。螺母的规格必须和螺丝一致（M4 螺丝配 M4 螺母）。
Pairs with a machine screw. The screw passes through both boards and the nut is tightened on the far side, clamping them like a sandwich. The nut size must match the screw (an M4 screw takes an M4 nut).
用在哪里 Where: 需要把两块板紧紧夹在一起、或者方便日后拆卸的木工/金属结构。/ Wood or metal assemblies that need a tight clamp or need to come apart later.
木头里的金属螺纹 Metal threads in wood: 木头上想反复拆装机械螺丝时，用 T 型螺母 (T-nut，从背面敲入) 或木用螺纹镶件 (Threaded insert for wood，用内六角拧进去)。/ To get a reusable machine-screw thread in wood, use a T-nut (hammered in from the back) or a threaded wood insert (screwed in with a hex key).
8.4 Heat-Set Insert 热熔预埋螺母（铜质小齿轮）
长相：黄色/铜色的金属小圆柱，外表布满滚花（凹凸纹路），内部是 M3 或 M4 等内螺纹。
Look: a small brass cylinder with a knurled (textured) outside and an internal thread such as M3 or M4.
是什么 What it is: 3D 打印和塑料件中最常用的配件。塑料直接拧螺丝很容易滑丝，预埋螺母给塑料件加上坚固的金属螺纹。它只适用于热塑性塑料（PLA、PETG、ABS 等），靠熔化塑料来固定，不能用在木头上；木头请用上一节的木用螺纹镶件。
The go-to accessory for 3D prints and plastic parts. Screws driven straight into plastic strip easily, and an insert gives the part a strong metal thread. It only works in thermoplastics (PLA, PETG, ABS and similar) because it holds by melting the plastic. It does not work in wood; use a threaded wood insert from the previous section instead.
怎么使用 How to use:
- 在 3D 打印件上预留一个比预埋螺母外径略小的直孔（看厂家给的孔径）。/ Leave a straight hole slightly smaller than the insert’s outside diameter (follow the maker’s spec).
- 把预埋螺母放在孔口。/ Set the insert on the hole.
- 用电烙铁（最好配专用压入头）加热螺母，铜受热后熔化周围塑料，顺势慢慢压入孔内，保持垂直。/ Heat the insert with a soldering iron (ideally with an insert tip). The hot brass melts the surrounding plastic and slides in; press slowly and keep it straight.
- 冷却后，塑料重新凝固并牢牢咬住外侧的滚花，之后就能像在金属上一样反复拧螺丝。/ Once cooled, the plastic hardens around the knurling and holds tight, so the screw can go in and out many times like in metal.
9. Buying Tips for Beginners 给新手的选购建议
- 螺纹类型 Thread type: 先确认说明书需要的是机械螺丝（配螺母或预埋件）还是自攻螺丝（直接拧进木头/塑料）。/ First check whether the manual calls for a machine screw (with a nut or insert) or a self-tapping screw (straight into wood or plastic).
- 公制还是英制 Metric or imperial: 欧洲、亚洲、宜家和大多数 3D 打印机用公制；美国五金店的木螺丝多为英制号数。/ Europe, Asia, IKEA and most 3D printers use metric; US hardware stores mostly sell wood screws in imperial gauges.
- 材质 Material: 室内用镀锌即可；户外、潮湿处用不锈钢（A2/304，海边用 A4/316）；黄铜漂亮但软，容易拧断，先用同规格钢螺丝攻一遍孔。/ Indoors, zinc-plated is fine. Outdoors or in damp spots, use stainless (A2/304, or A4/316 near the sea). Brass looks good but is soft and snaps easily, so cut the thread first with a steel screw of the same size.
- 起子头 Bits: 买一套包含 PH2、PZ2、T20/T25、方头 #2 和常用内六角的起子头套装，基本覆盖日常需求。/ A bit set with PH2, PZ2, T20/T25, square #2 and common hex keys covers almost everything day to day.
- 代替方案 Alternative: 说明书写 “Alternatively, use superglue” 表示此处受力极小。如果手头暂时没有 M3 螺丝，用 502 或快干胶 (Superglue) 粘合完全可行，只是之后不能拆。/ When a manual says “Alternatively, use superglue”, that joint carries almost no load. Without an M3 screw on hand, superglue works fine, but the joint can no longer be taken apart.
10. Common Mistakes 常见错误
- 起子头不匹配或太小，把螺丝头拧花。/ Using a mismatched or undersized bit and stripping the head.
- 电钻扭力开太大，拧过头把木头或塑料里的螺纹拧滑。最后几圈用手拧或调低离合档位。/ Setting the drill torque too high and stripping the thread in wood or plastic. Finish the last turns by hand or lower the clutch setting.
- 用石膏板螺丝做家具。/ Building furniture with drywall screws.
- 硬木或板端不打预钻孔，导致开裂。/ Skipping the pilot hole in hardwood or end grain and splitting the wood.
- 上板不打过孔，结果两块板之间留缝。/ Skipping the clearance hole in the top board and leaving a gap between boards.
- 公制和英制螺丝混用。/ Mixing metric and imperial threads.
Key Takeaways
- 先分清机械螺丝（配螺母/预埋件）和自攻螺丝（直接拧进材料）。/ First tell machine screws (need a nut or insert) from self-tapping screws (go straight into material).
M4 x 20= 外径 4 mm、长 20 mm；沉头量全长，其他头型从头下量。/M4 x 20= 4 mm diameter, 20 mm long; countersunk heads are measured overall, other heads from under the head.- 起子头要和驱动槽完全匹配：十字 PH、米字 PZ、梅花 T、方头 R。/ Match the bit to the recess exactly: Phillips PH, Pozidriv PZ, Torx T, square R.
- 木工：上板打过孔、下板打预钻孔、沉头螺丝配沉头孔。/ Woodworking: clearance hole in the top board, pilot hole in the bottom board, countersink for flat heads.
- 平垫圈分散压力，弹簧垫圈防松，螺母对夹，热熔预埋螺母给塑料加金属螺纹。/ Flat washers spread load, lock washers resist loosening, nuts clamp, heat-set inserts give plastic a metal thread.
References
- ISO 4762 / ISO 10642 (metric socket head and countersunk screw dimensions)
- Kreg Tool pocket-hole screw selection chart
- Fastenal Engineering & Design Support: tap drill and clearance hole charts
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