Screw specification definition and understanding 一. Thread typeA: triangular thread (60 degrees) : combining/lock B: work triangular thread (55 degrees) : combine/lock C: trapezoidal thread (30 or 29 degrees) : power transmission D: square thread (90 degrees) : power transmission 二. Common screw types: A: the Machine Screw, Machine Screw B: Tapping Screw, self-tapping Screw (points used in metal and used in plastic two) B - 1: Sheet Metal Tapping Screw. (self-tapping self-drilling screws) B - 2: Plastic Tapping Screw. (for plastics, self Tapping Screw) C: Wooden Screw, wood Screw D: Drywall Screw, concrete Screw 三.Common screw material:  A. ow Carbon Steel, low Carbon Steel B. SS - 304: Stainless Steel 304 C. SS - 302: Stainless Steel 302: structure has good toughness D. 5052: Aluminum alloy 5052 E. Brass, Brass F. Bronze, Bronze G. UNS C11000 Copper, antimony, Copper 四. Common screw specifications and sign: A: metric screw B: ul screw C: the imperial screws A: Metric screw machinery: Metric Ex: the M3 x 6 - P P B: mechanical screw M3, 6 mm long, cross, circle flat head, black plating. The Finish Code: processing appearance specifications The Head Code: the Head shape The Thread Code Screw type Drive Code: cross cutting head, characteristic model The screw Length Code: Length (mm) A - 1: Thread Code: screw type Metric screw marked with screw diameter screw type directly, Such as M3 or screw diameter of 3.00 mm.;The M4 screw outside diameter is 4.00 mm. Metric Thread Size x Pitch: Note: metric screw in screw type rear, can sometimes indicate the screw tooth pitch. Such as M3x0. 5, M4x0. 70, M5x0. 8, M6x1. But because the standard specification, usually. A - 2: Length Code: screw Length: Metric screws, marked screw length directly, the unit is mm. The total length of screw, only the head count of the following length, excluding the head height. But flat head screw, the screw of the total length including head height. A - 3: Drive Code/cross cutting head, characteristics. Commonly used specifications are as follows: A. Slotted: a word (Minus) B. Phillips: cross (Plus) C. Phil - Slot: a word/cross D. Hex Scoket: Allen E. One Way: One Way (can be locked into only, not for exit) A - 4: the Head Code/Head shape. Commonly used specifications are as follows: A. Flat, Flat head (flush after lock into the top and work pieces) B. Oval: salad C. Round, Round head D. Pan: round flat head E. Truss: great circle flat head F. Hex: Hex head. A - 5: Finish Code/processing appearance. Commonly used specifications are as follows: A. Z: Zine - Plated: galvanized B. Ni, Ni - Plated, nickel Plated C. Tin - Plated, Tin Plated D. Zine Plated/Green Iridite: galvanized Green film processing. E. Radiant Plated: colorful plating F. Passivate: antioxidant treatment. G. Alodial Finish: no appearance Metric self Tapping screw, Tapping affixed to its name directly behind the Type. Ex: the M3 x 6 - PPB, Tapping Type: The M3 tapping screw, 6 mm long, cross, circle flat head, black plating. General with don't or labeling products, then judge for Sheet Metal or plastic parts are used. B: ul screw. A. with mash commonly labeled as # 2-56, 4-40 #, # 6-32, # 32, # 8-10-24...Etc. B. or expressed in inch diameter, 40-56 as 0.086, 0.086, 0.086-32, 0.164 to 0.190-24-32,...Etc. Ex: 632-8 - P P B: The Finish Code: processing appearance specifications The Head Code: the Head shape Drive Code: cross cutting head, characteristics of the model Length Code: screw Length The screw Thread Code: model B - 1: Thread Code: screw type Commonly used specifications are as follows: 56 (a. # 2-0.086-56) : 56 teeth 2 times B # 4-40 (0.112-40) : four times 40 teeth C # 6-32 (0.138-32) : 6 32 teeth D. # 8-32 (0.164-32) : 8 32 teeth E. # 10-24 (0.190-24) : 10 times of 24 teeth Tooth number of teeth per inch * * *. * * * B - 2: Length Code: screw Length Ul screw length must be approved by conversion, is metric mm size. Conversion formula: (Length Code / 32) x 25.40 = metric mm Length B - 3-4 B, B - 5: the way the same as the metric system. C: the imperial screws: C - 1: Thread Code: Labeling is the denominator of 8, and then directly according to the mash of molecules. Ex: 1/8 x 0.50 PPB: 1 tooth screw x 0.50 "long, PPB Ex: 5/16 x 0.50 x 0.50 PPB PPB = 2.5/8:2 and a half tooth screw x 0.50 "long, PPB Ex: 5/32 x 0.50 x 0.50 PPB PPB = 1.25/8:1 screw x 0.50 "in about two and a half mile long, PPB Ex: 1/4 x 0.50 x 0.50 PPB PPB = 2/8:2 points tooth screw x 0.50 "long, PPB Note: sometimes labeled coarse thread or fine teeth. UNF) : fine thread: electronics industry is relatively commonly used. UNC: coarse thread: heavy mechanical structure is relatively commonly used. Ex: 3/8 x 0.50, UNF, PPB: 3 points fine thread screw x 0.50 "long, PPB. C - 2: Length of Code: For inch mark must be multiplied by 25.40 conversion for mm