How to measures screws thread of annotation format

Screw for daily life indispensable industrial necessities: such as camera, glasses, watches and clocks, electronic use tiny screw; Television, electrical products, instruments, furniture and other general screw; As to engineering, building, bridge using large screws, nuts; Transportation equipment, aircraft, trains, cars, etc for the size of the screw. How to measure the screw? Screws as an inclined plane circular rotation and the friction of physics and mathematics principle, fastening step by step implements part of the tool. In general are need to closely integrated with fasteners. So in the process of screw used for the selection of thread and size, is very important. Below is based on to illustrate how to measure the screw thread of annotation format. 

   In fact, for any screw, measurement is on the determination of thread, because different screws, screw thread of the format is different. In general, the thread of the tag label format for: thread code - tolerance zone code (pitch diameter, top diameter) - screw length l) tolerance zone code by the Numbers and letters (internal thread in capital letters, external thread in lowercase), such as 7 h, 6 g, etc., should be noted, 7 h, 6 g, etc. On behalf of the thread tolerance, and H7, g6 cylinder tolerance code. 2) screw length regulations for short (S), medium (N), length (L) 3 kinds. In general, not marked screw length, its thread tolerance zone according to the medium spiral length (N). When necessary, can be loaded with screw length code S or L, such as "M20-5 g6g - L". When special needs, can indicate the screw length values, such as "M20-5 g6g - 30". Label format for common thread: characteristic code (cylindrical pipe thread in G, tapered pipe thread with NPT) + code + tolerance grade code size, rotate to G1A - LH says inch threaded pipe thread sealing, number 1 in size, A left-handed, tolerance grade for A grade. Rcl / 2 inch thread taper pipe thread sealing, 1/2 in size code, right. So, after how to measures the screws, as long as know the corresponding data, can very good judgement and measure the size of the screw.