Hex socket head cap screw P=3(Coarse Steel Trivalent black(Black) 3 X 20 Pitch 0.5

This is a bolt with a hexagonal socket in a cylindrical head. Tightening is performed using a hex key (Allen wrench).
In most cases, it is used without a nut. It is also known as a cap screw or socket screw.
When fastening a hex bolt, a wrench requires working space, whereas a hex key does not.

Cap Bolt　
Hex Socket Head Cap Screw Encyclopedia
Cap Bolt　P=3

• Hex socket head cap screw P=3 Coarse pitch
• P=3 (With spring washer + JIS flat washer)
• Nominal thread diameter M3
• Length under head (L) 20.0
• Coarse pitch 0.5
• Head diameter (dk) Nominal: 5.5 Max: 5.68 Min: 5.32
• Head height (k) Nominal: 3 Min: 2.86
• Hex socket width across flats (s) Nominal: 2.5 Max: 2.58 Min: 2.52
• Hex socket depth (t) Min: 1.3
• Flat washer (D x t) 8 x 0.5
• Spring washer (d) Max: 5.4
• Spring washer (b x t) 1.1 x 0.7
• Incomplete thread section Max: 2.8
• Partial thread range L35 or above
• Partial thread length 30~33
• * Full thread length = L dimension - Incomplete thread section length