Hex Cap Screws are an externally threaded mechanical device 1/4" diameter or larger, with a trimmed hex head and a washer face on the bearing surface. They come in different grades (or hardnesses). Grade 2-medium or low carbon steel, a Grade 5 has greater tensile strength than a grade 2 and a Grade 8 which has a greater tensile strength than a Grade 5. Also available in 18-8 stainless for corosion resistence and in 316 Stainless which is even more corroision resistence than 18-8.

Mechanical and Material
Requirements for Grades 2, 5 & 8 Hex
Head Cap Screws

Abstract of SAE J429 1985

Grade Designation	Products	Nominal Size Dia., In.	Full Size Bolts, Screws Studs, Sems		Machine Test Specimens of Bolts, Screws and Studs				Surface Hardness	Core Hardness		Grade Identification Marking L
			Proof Load (Stress) psi	Tensile Strength (Stress) Min., psi	Yield Strength (Stress) Min., psi	Tensile Strength (Stress) Min., psi	Elongation Min., %	Reduction of Area Min, %	Rockwell 30N Max.	Rockwell
										Min.	Max.
2	Bolts, Screws, Studs	1/4 thru 3/4 Over 3/4 to 1-1/2	55,000 33,000	74,000 60,000	57,000 36,000	74,000 60,000	18 18	35 35	-- --	B80 B70	B100 B100	None
5	Bolts, Screws, Studs	1/4 thru 3/4 Over 3/4 to 1-1/2	85,000 74,000	120,000 105,000	92,000 81,000	120,000 105,000	14 14	35 35	54 50	C25 C19	C34 C30
8	Bolts, Screws, Studs	1/4 thru 1-1/2	120,000	150,000	130,000	150,000	12	35	58.6	C33	C39