Machinery's Handbook, 31st Edition
Clearance Holes
1741
Clearance Holes for Bolts, Screws, and Studs The Standard ANSI/ASME B18.2.8-1999 (R2017) covers the recommended clearance hole sizes for #0 through 1.5 inch and M1.6 through M100 metric fasteners in three classes of clearance using a close-, normal-, and loose-fit category. The clearance hole tolerances for both inch and metric holes are based on ISO 286, ISO System of Limits and Fits , using tolerance class H12 for close-fit, H13 for normal-fit, and H14 for loose-fit clearance holes. The clearances provided by the three classes of fit are based on regularly stepped clearances as listed in Table 1a for inch and Table 2b for metric. Inch Fasteners.— The hole sizes for inch fasteners are patterned after US common usage and the general clearances translated from the metric standard. The hole tolerances are based on the ISO System of Limits and Fits , as required by ISO 273. The tabulated drill and hole sizes, Table 1a, lists the inch fastener clearance hole recom mendations. The recommended drill sizes for inch fasteners are tabulated by nominal drill designation as letter, numbers, or fractional sizes. The drill sizes were selected to provide as nearly as practical a step-patterned clearance size for the minimum recommended hole (Table 1b ). The maximum recommended hole size is based on standard hole tolerances. Table 1a. Clearance Holes for Inch Fasteners ANSI/ASME B18.2.8-1999 (R2017)
Normal
Close
Loose
Hole Diameter
Hole Diameter
Hole Diameter
Nominal Drill Size
Nominal Screw Size
Nominal Drill Size
Nominal Drill Size
Min.
Max.
Min.
Max.
Min.
Max.
0.094 0.104 0.104 0.114 0.116 0.126 0.128 0.140 0.144 0.156 0.172 0.184 0.185 0.197 0.213 0.225 0.297 0.311 0.359 0.373 0.422 0.438 0.484 0.500 0.609 0.625 0.734 0.754 0.906 0.926 1.031 1.051 1.156 1.181 1.312 1.337 1.438 1.463 1.609 1.634 1.734 1.759
#0 #1 #2 #3 #4 #5 #6 #8
#48 #43 #38 #32 #30 5 ∕ 32 #18 #9 #2 9 ∕ 32 11 ∕ 32 13 ∕ 32 15 ∕ 32
0.076 0.082 0.089 0.095 0.102 0.108 0.116 0.122 0.128 0.135 0.156 0.163 0.170 0.177 0.196 0.203 0.221 0.228 0.281 0.290 0.344 0.354 0.406 0.416 0.469 0.479 0.562 0.572 0.688 0.698 0.812 0.824 0.938 0.950 1.094 1.106 1.219 1.235 1.344 1.360 1.500 1.516 1.625 1.641
#51 #46 3 ∕ 32 #36 #31 9 ∕ 64 #23 #15 #5 17 ∕ 64 21 ∕ 64 25 ∕ 64 29 ∕ 64 17 ∕ 32 21 ∕ 32 25 ∕ 32 29 ∕ 32 1 1 ∕ 32 1 5 ∕ 32 1 9 ∕ 32 1 7 ∕ 16 1 9 ∕ 16
0.067 0.071 0.081 0.085 0.094 0.098 0.106 0.110 0.120 0.124 0.141 0.146 0.154 0.159 0.180 0.185 0.206 0.211 0.266 0.272 0.328 0.334 0.391 0.397 0.453 0.460 0.531 0.538 0.656 0.663 0.781 0.789 0.906 0.914 1.031 1.039 1.156 1.164 1.281 1.291 1.438 1.448 1.562 1.572
3 ∕ 32 #37 #32 #30 #27 11 ∕ 64 #13 19 ∕ 64 23 ∕ 64 27 ∕ 64 31 ∕ 64 #3
#10
B 0.238 0.250
1 ∕ 4
5 ∕ 16
3 ∕ 8
7 ∕ 16
9 ∕ 16
1 ∕ 2 5 ∕ 8 3 ∕ 4 7 ∕ 8
39 ∕ 64 47 ∕ 64 29 ∕ 32 1 1 ∕ 32 1 5 ∕ 32 1 5 ∕ 16 1 7 ∕ 16 1 39 ∕ 64 1 47 ∕ 64
11 ∕ 16 13 ∕ 16
15 ∕ 16 1 3 ∕ 32 1 7 ∕ 32 1 11 ∕ 32
1
1 1 ∕ 8 1 1 ∕ 4 1 3 ∕ 8 1 1 ∕ 2
1 1 ∕ 2 1 5 ∕ 8
Table 1b. Inch Clearance Hole Allowances
Fit Classes
Fit Classes
Nominal Screw Size
Nominal Screw Size
Normal
Close 0.008
Loose
Normal
Close
Loose
1
#0 – #4 #5 – 7 ∕ 16
1 ∕ 32 1 ∕ 32 1 ∕ 16
5 ∕ 32 3 ∕ 16
1 ∕ 64 1 ∕ 32 1 ∕ 16 1 ∕ 16
1 ∕ 32 3 ∕ 64 7 ∕ 64 5 ∕ 32
3 ∕ 32 3 ∕ 32
1 1 ∕ 8 , 1 1 ∕ 4 1 3 ∕ 8 , 1 1 ∕ 2
1 ∕ 64 1 ∕ 32 1 ∕ 32
1 ∕ 2 , 5 ∕ 8 3 ∕ 4 , 7 ∕ 8
1 ∕ 8
15 ∕ 64
…
… … …
Dimensions are in inches.
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