推荐回答（5个）
1、M3×0.5螺纹小径是2.459mm，螺纹大径是2.675mm；M3×0.35螺纹小径是2.621mm，螺纹大径是2.773mm。
2、M3螺纹参照GB/T 196-2003《普通螺纹基本尺寸》，本标准依据GB/T 192-2003和GB/T 193-2003规定了普通螺纹（一般用途米制螺纹）的基本尺寸。
扩展资料：
常见螺丝
<一>头部剖沟,螺丝刀咀型:
a. Slotted: 一字b. Phillips: 十字
c. Phil-Slot: 一字/十字
d. Hex Scoket: 内六角
e. One Way: 单向(只可锁入,不可退出)
<二>螺丝头头型:
a. Flat: 平头(锁入后,顶部与工作件齐平)
b. Oval: 色拉头
c. Round: 圆头
d. Pan: 圆扁头/盘头
e. Truss: 大圆扁头
f. Hex : 六角头
<三> 外观表面处理:
a. Z: Zine-Plated: 镀锌
b. Ni: Ni-Plated: 镀镍
c. Tin-Plated: 镀锡
d. Zine Plated / Green Iridite: 镀锌绿膜处理.
e. Radiant Plated: 镀五彩
f. Passivate: 抗氧化处理
g. Alodial Finish: 无外观处理
<四>螺纹规格:
a. 公制螺丝
Ex: M6 x 8 - PPB
M6x1机械牙螺丝, 8mm长, 十字沟槽, 圆扁头, 镀黑.
b. 美制螺丝
美规螺丝一般以番号标示,
如#2-56, #4-40, #6-32, #8-32, #10-24…etc.
Ex: #2-56 (0.086-56): 2 番56 牙
Ex: #4-40 (0.112-40) : 4 番40 牙
Ex: #6-32 (0.138-32) : 6 番32 牙
Ex: #8-32 (0.164-32) : 8 番32 牙
Ex: #10-24 (0.190-24): 10 番24 牙
***牙数为每英寸牙的数量,长度须经过换算才是公制mm 尺寸,1"(英寸)=25.4mm(毫米).***
c. 英制螺丝:
标示皆将分母为8, 再直接称分子之番号.
Ex: 1/8 x 0.50 - PPB : 1 分牙螺丝钉x 0.50” 长, PPB
Ex: 5/16 x 0.50- PPB = 2.5/8 x 0.50 - PPB : 2 分半牙螺丝钉x 0.50” 长, PPB
Ex: 5/32 x 0.50- PPB =1.25/8 x 0.50 - PPB : 1 分2 厘半螺丝钉x 0.50” 长, PPB
Ex: 1/4 x 0.50- PPB= 2/8 x 0.50 - PPB : 2分牙螺丝钉x 0.50” 长, PPB
注: 有时会标示粗牙或细牙
UNF: 细牙:电子业较常用
UNC:粗牙: 重机械结构较常用
Ex: 3/8 x 0.50 UNF -PPB : 3分细牙螺丝钉x 0.50” 长, PPB.
或以英制外径表示,
如0.086-56, 0.112-40 , 0.138-32 , 0.164-32 , 0.190-24…etc.
Ex: 632 - 8 - PPB.
***英制螺丝外径和长度长度须经换算才是公制mm 尺寸,1"(英寸)=25.4mm(毫米).***
1. M3×0.5螺纹小径是2.459mm，螺纹大径是2.675mm；M3×0.35螺纹小径是2.621mm，螺纹大径是2.773mm。
2. M3螺纹参照GB/T 196-2003《普通螺纹基本尺寸》，本标准依据GB/T 192-2003和GB/T 193-2003规定了普通螺纹（一般用途米制螺纹）的基本尺寸。
本标准适用于一般用途的机械紧固螺纹联接，其螺纹本身不具有密封功能。
1、国标常用的 M3×0.5的螺丝外径是在2.88-2.98之间，内径为2.60。
2、攻螺纹时，底孔打Φ2.5
M3螺丝是粗牙螺纹标准螺距是0.5mm，内螺纹内径2.5mm，外螺纹外径3mm负0.02-0.12，中径:2.675mm.
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