ASME B18.3 Hexagon Socket Button Head Cap Screws

ASME B18.3 Hexagon Socket Button Head Cap Screws

ASME B18.3 Dimensions of Hexagon Socket Button Head Cap Screws

Nominal Size
(Basic Screw
Diameter)		 Head
Diameter, A		 Head
Height, H		 Head
Side
Height, S
(Ref.)		 Nominal
Hexagon
Socket Sizze, J		 Minimum
Key
Engagement, T		 Fillet
Extension,
F		 Nominal
Maximum
Standard
Length, L
Max Min Max Min Max. Min
0 (0.0600) 0.114 0.104 0.032 0.026 0.010 ... 0.035 0.020 0.080 0.070 0.50
1 (0.0730) 0.139 0.129 0.039 0.033 0.010 ... 0.050 0.028 0.093 0.083 0.50
2 (0.0860) 0.164 0.154 0.046 0.038 0.010 ... 0.050 0.028 0.106 0.096 0.50
3 (0.0990) 0.188 0.176 0.052 0.044 0.010 1/16 0.062 0.035 0.119 0.109 0.50
4 (0.1120) 0.213 0.201 0.059 0.051 0.015 1/16 0.062 0.035 0.132 0.122 0.50
5 (0.1250) 0.238 0.226 0.066 0.058 0.015 5/64 0.078 0.044 0.145 0.135 0.50
6 (0.1380) 0.262 0.250 0.073 0.063 0.015 5/64 0.078 0.044 0.158 0.148 0.063
8 (0.1640) 0.312 0.298 0.087 0.077 0.015 3/32 0.094 0.052 0.194 0.184 0.75
10 (0.1900) 0.361 0.347 0.101 0.091 0.020 1/8 0.125 0.070 0.220 0.210 1.00
1/4 (0.2500) 0.437 0.419 0.132 0.122 0.031 5/32 0.156 0.087 0.290 0.280 1.00
5/16 (0.3125) 0.547 0.527 0.166 0.152 0.031 3/16 0.188 0.105 0.353 0.343 1.00
3/8 (0.3750) 0.656 0.636 0.199 0.185 0.031 7/32 0.219 0.122 0.415 0.405 1.25
7/16 (0.4375) 0.765 0.746 0.231 0.218 0.031 1/4 0.250 0.140 0.478 0.468 1.50
1/2 (0.5000) 0.875 0.851 0.265 0.245 0.046 5/16 0.312 0.175 0.560 0.540 2.00
5/8 (0.6250) 1.000 0.970 0.331 0.311 0.062 3/8 0.375 0.210 0.685 0.665 2.00
3/4 (0.7500) 1.125 1.105 0.375 0.355 0.062 7/16 0.437 0.245 0.740 0.720 2.50

GENERAL NOTES:
(a) This product is designed and recommended for light fastening applications such as guards, hinges, etc. It is not suggested for use in critical high strength applications where socket head cap screws should normally be used.
(b) For additional requirements, refer to Notes (6) through (14) and section 2, General Data, of this Standard.

NOTES:
(1) Length. The length of the screw shall be measured, parallel to the axis of the screw, from the plane of the bearing surface under the head to the plane of the flat of the point. The portion of the screw contained within dimension, L, is commonly called the shank. The basic length dimension on the product shall be the nominal length expressed as a two-place decimal.

(2) Standard Lengths. Standard length increments for socket button head cap screws shall be as tabulated below.

Nominal Screw Length Standard Length Increment
0.13 through 0.25
0.25 through 1.00
1.00 through 2.00		 0.06
0.13
0.25

(3) Length Tolerances. Allowable tolerance on length shall be as tabulated below.

Nominal Screw Size, Tolerance on Length
Nominal Screw Length 0 Through 3/8, Incl. 1/2 Through 5/8 Incl.
Up to 1.00, Incl. -0.03 -0.03
Over 1.00 to 2.00, Incl. -0.04 -0.06
Over 2.00 -0.04 -0.06

(4) Thread Length. For screws of nominal lengths equal to or shorter than standard maximum lengths, L, listed in this Table, the complete (full-form) threads, measured with a thread ring gage having the thread chamfer and/or counterbore removed, shall extend to within two pitches (threads) of the bearing surface of the head. For longer screws, the length of the complete thread shall, at the option of the manufacturer, be between the minimum limit of twice the basic screw diameter plus 0.50 in. and the maximum limit within two pitches (threads) of the head. The unthreaded portion of the screw shall be at nominal diameter. The tolerance on the unthreaded portion (body diameter) of the screw shall be the same as Body Diameter, D, Table 1, Hexagon Socket Head Cap Screws.

(5) Screw Point Chamfer. The point shall be flat or slightly concave and chamfered. The plane of the point shall be approximately normal to the axis of the screw. The chamfer shall extend slightly below the root of the thread, and the edge between flat and chamfer may be slightly rounded. The included angle of the point should be approximately 90 deg. Chamfering of screw sizes up to and including size 8 (0.164 in.) and lengths below 0.75d shall be optional.

(6) Nominal Size. Where specifying nominal size in decimals, zeros preceding decimal and in the fourth decimal place shall be omitted.

(7) Fillet. The form of the fillet shall be optional, provided it flairs into the bearing surface between the minimum and maximum diameter, F. The fillet shall be a smooth and continuous curve having a bearing surface juncture radius not less than that tabulated below.

Nominal Screw Size Minimum Juncture Radius Nominal Screw Size Minimum Juncture Radius
0 0.002 10 0.006
1 0.003 1/4 0.007
2 0.003 5/16 0.009
3 0.004 3/8 0.0012
4 0.004 7/16 0.014
5 0.005 1/2 0.016
6 0.005 5/8 0.021
8 0.006 3/4 0.025

(8) Head Height. Tabulated head heights represent metal-to-metal measurements; that is, the truncation of the rounded surface caused by the socket is not considered part of the head height.

(9) See Table 18 for hexagon socket dimensions and Mandatory Appendix I for gaging of hexagon sockets.

(10) Bearing Surface. The plane of the bearing surface shall be perpendicular to the axis of the shank within 2 deg obtained by holding the screw on the body or major thread diameter within 1 diameter of the bearing surface of the head, but beyond the maximum length of the fillet, F, rotating 360 deg, and inspecting on an optical comparator, or comparable inspection equipment.

(11) Runout
(a) The runout of the head with the axis of the shank shall be within 3% of the maximum basic screw diameter dimension, D, or 0.008 in., whichever is greater.
Runout for
(a) above is defined as the full indicator movement (FIM) obtained by holding the screw on the body or major thread diameter next to the head, but beyond the maximum length of the fillet, F, rotating the screw 360 deg, with the indicator riding on the outer surface of the head on the rounded portion, adjacent to, but not on the extreme periphery of, the head.
(b) The runout of the socket with the axis of the shank of the screw shall be within 3% of the maximum screw diameter, D, or 0.005 in., whichever is greater for nominal sizes through 1⁄2 in. diameter and 6% for nominal sizes above 1⁄2 in. diameter.
Runout for
(b) above is defined as the full indicator movement (FIM) obtained by holding the screw on the body or major screw thread diameter within 1 diameter of the bearing surface of the head, but beyond the maximum length of the fillet, F, rotating 360 deg, indicating on each of the hexagon flats.

(12) Threads. Threads shall be Unified external threads with radius root: Class 3A UNRC and UNRF Series.
Acceptability shall be based on System 22, ASME B1.3.
Class 3A does not provide a plating allowance.

(13) Material
(a) Steel, Alloy. Button head cap screws shall be fabricated from an alloy steel and shall conform in all respects to ASTM F835.
(b) Steel, Corrosion-Resistant. Button head cap screws shall be fabricated from austenitic corrosion-resistant steel and shall conform to ASTM F879.

(14) Designation. To promote uniformity and understanding in communications relating to products conforming to this Standard, it is recommended that Hexagon Socket Button Head Cap Screws be designated in accordance with the following data, preferably in the sequence shown:
(a) product name
(b) designation of the standard
(c) nominal size (number, fractional or decimal equivalent)
(d) thread pitch
(e) nominal length (fractional or decimal equivalent)
(f) material
(g) protective finish, if required
EXAMPLES:
Hexagon Socket Button Head Cap Screws, ASME B18.3, 10-32  3⁄4 , Alloy Steel
Hexagon Socket Button Head Cap Screws, ASME B18.3, 0.190-32  0.750, Alloy Steel, Zinc Plated. (For plated products, see para.
1.7, Introductory Notes.)
For the recommended B18 part identifying numbering (PIN) system, see ASME B18.24.