TABLE 9.4 PREFERRED SCREW LENGTHS AND HEADS FOR MACHINE SCREWS
NOMINAL SIZE OF SCREW - NUMBERS AND FRACTIONAL SIZES
Machine	2	4	6	8	10	1/4	5/16	3/8
Screw				Threads	Per Inch			
Lengths	56	40	32	32	24	20	18	16
Inches					32			
1/8	FRPS	FRPS	RPS	RPS				
3/16	FRP	FRP						
1/4	FRPS	FRPS	FRPS	FRPS	FRPS			
5/16	FRP	FRP						
3/8	FRPS	FRPS	FRPS	FRSP	FRPS	HFRPS	HFRPS	
1/2	FRPS	FRPS	FRPS	FRPS	FRPS	HFRPS	HFRPS	
3/4	FRPS	FRPS	FRPS	FRPS	FRPS	HFRPS	HFRPS	FRHS
1	FRPS	FRPS	FRPS	FRPS	FRPS	HFRPS	HFRPS	FRHS
1 1/4		FRPS	FRPS	FRPS	FRPS		HFRPS	FRHS
1 1/2			FRPS	FRPS	FRPS	HFRPS	HFRPS	FRHS
1 3/4			FRPS	FRPS	FRPS		HFRPS	FHS
2			FRPS	FRPS	FRPS	HFRPS	HFRPS	FRHS
2 1/2						HFRPS	FR	FRHS
3						HFRPS	FR	FHS
3 1/2							H	
4							H	

H - HEX HEAD
F - FLAT HEAD 82 DEGREES COUNTERSINK
R - ROUND HEAD
P - FILLISTER HEAD
S - SOC HEAD