BRITISH Machine Screws Machinery's Handbook, 31st Edition British Standard Machine Screws and Nuts BS 450:1958 (obsolescent) and BS 1981:1953
1809
B Length
B
Length
H
H
82° 80° or
90° 92°
D
A
A
D
J
J
80 ° Countersunk head screw (Unified) 90 ° Countersink head screw (BSW & BSF)
Round head screw (BSW & BSF)
B
Length
B Length
H
H
82° 80° or
90° 92°
A
A
D
D
J
J
80 ° Raised countersunk head screw (Unified) 90 ° Raised countersunk head screw (BSW & BSF)
Mushroom head screw (BSW & BSF)
B
Length
B
Length
H
A
A
D
C
D
30°
J
Pan head screw (Unified, BSW & BSF)
Hexagon head screw (Unified)
B
Length
B
Length
0.015
H
A
D
F
30°
J
Cheese head screw (BSW & BSF)
Hexagon head screw (Unified) alternate design
B
Length
A E
E
E
A
H
30° 30°
C
C
A
D
30°
D
D
Pressed Type Precision Type (Optional)
J
Raised cheese head screw (Unified) Hexagon machine screw nut (Unified) *Countersinks to suit the screws should have a maximum angle of 80 ° (Unified) or 90 ° (BSF and BSW) with a negative tolerance. †Unified countersunk and raised countersunk head screws 2 inches long and under are threaded right up to the head. Other Unified, BSW and BSF machine screws 2 inches long and under have an unthread shank equal to twice the pitch. All Unified, BSW and BSF machine screws longer than 2 inches have a minimum thread length of 1 3 ∕ 4 inches.
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