ASME B18.5 Step Bolts

                                                                                                  

Nominal Size	Body Dia., E		Corner Rad. on Square, Q	Width of Square, O		Depth of Square, P		Dia. of Head, A		Height of Head, H		Fillet Radius, R
	Max.	Min.	Max.	Min.	Min.	Max.	Min.	Max.	Min.	Max.	Min.	Max.
ASME B18.5 - No. 10	0.199	0.182	0.031	0.199	0.185	0.125	0.094	0.656	0.625	0.114	0.094	0.031
ASME B18.5 - 1⁄4	0.26	0.237	0.031	0.26	0.245	0.156	0.125	0.844	0.813	0.145	0.125	0.031
ASME B18.5 - 5⁄16	0.324	0.298	0.031	0.324	0.307	0.187	0.156	1.031	1	0.176	0.156	0.031
ASME B18.5 - 3⁄8	0.388	0.36	0.047	0.388	0.368	0.219	0.188	1.219	1.188	0.208	0.188	0.031
ASME B18.5 - 7⁄16	0.452	0.421	0.047	0.452	0.431	0.25	0.219	1.406	1.375	0.239	0.219	0.031
ASME B18.5 - 1⁄2	0.515	0.483	0.047	0.515	0.492	0.281	0.25	1.594	1.563	0.27	0.25	0.031
ASME B18.5 - 5⁄8a	0.642	0.605	0.078	0.642	0.616	...	...	...	...	...	...	...
ASME B18.5 - 3⁄4a	0.768	0.729	0.078	0.768	0.741	...	...	...	...	...	...	...
a These sizes pertain to 114 degree countersunk square neck bolts only. Dimensions given in last seven columns to the right are for these bolts only. All dimensions are in inches unless otherwise specified. Threads are Unified Standard, Class 2A, UNC Series, in accordance with ANSI B1.1. For threads with additive finish, the maximum diameters of Class 2A shall apply before plating or coating, whereas the basic diameters (Class 2A maximum diameters plus the allowance) shall apply to a bolt after plating or coating. Bolts are designated in the sequence shown: nominal size (number, fraction or decimal equivalent); threads per inch; nominal length (fraction or decimal equivalent); product name; material; and protective finish, if required. For example   1⁄2 - 13 × 3 Round Head Square Neck Bolt, Steel .375-16 × 2.50 Step Bolt, Steel, Zinc Plated