This page provides standard bolt hole centres, back marks and edge distances for structural steel sections including channels, angles, universal beams and columns. These dimensions are used in structural and mechanical design to ensure adequate bolt access, correct positioning relative to the centroid, and sufficient edge distance to prevent failure.
The data is commonly used in fabrication drawings, connection design and structural detailing.
These bolt hole centre and back mark dimensions are commonly used in:
The back mark is the distance from the back of an angle or channel web to the centre of a hole through the leg or flange. This dimension is selected taking into account, access for tightening the bolt using an appropriate spanner, being close to centroidal axis ,and provision of required edge distance The distance between centres of holes in flanges of joists, universal columns and Universal beams is selected to provide accessibility and acceptable edge distance.
All Dimensions in mm
Maximum recomended bolt sizes shown in brackets
dimensions in mm
|
Nominal Flange Wdith
|
S1
Back Mark
|
Edge Dist
|
Recommended Bolt dia
|
|
102
|
55
|
47
|
24
|
|
89
|
55
|
34
|
20
|
|
76
|
45
|
31
|
20
|
|
64
|
35
|
29
|
16
|
|
51
|
30
|
21
|
10
|
|
38
|
22
|
-
|
|
All Dimensions in mm
Maximum recomended bolt sizes shown in brackets
| Nominal leg | S1 | S2 | S3 | S4 | S5 | S6 |
| 25 | 15 | - | - | - | - | - |
| 30 | 20 | - | - | - | - | - |
| 40 | 23 | - | - | - | - | - |
| 45 | 25 | - | - | - | - | - |
| 50 | 28 (12) | - | - | - | - | - |
| 60 | 35 (16) | - | - | - | - | - |
| 65 | 35 (20) | - | - | - | - | - |
| 70 | 40 (20) | - | - | - | - | - |
| 75 | 45 (20) | - | - | - | - | - |
| 80 | 45 (20) | - | - | - | - | - |
| 90 | 50 (24) | - | - | - | - | - |
| 100 | 55 (24) | - | - | - | - | - |
| 120 | - | 45 (16) | 50 (16) | - | - | - |
| 125 | - | 45 (20) | 50 (20) | - | - | - |
| 150 | - | 55 (20 ) | 55 (20) | - | - | - |
| 200 | - | 75(30) | 75(30) | 55 (20) | 55 (20) | 55 (20) |
All Dimensions in mm
Maximum recomended bolt sizes shown in brackets
| Flange width | Min. for Accessiblility |
Maximum for Edge dist |
S1 | S2 | S3 | S4 |
| Joists | ||||||
| 44 | 27(5) | 30 | 30 | - | - | - |
| 64 | 38(10) | 39 | 40 | - | - | - |
| 76 | 48(10) | 51 | 48 | - | - | - |
| 89 | 54 (12) | 59 | 56 | - | - | - |
| 102 | 60 (16) | 62 | 60 | - | - | - |
| 114 | 66(16) | 74 | 70 | - | - | - |
| 127 | 72(20) | 77 | 75 | - | - | - |
| 152 | 75(20) | 102 | 90 | - | - | - |
| 203 | 91(24) | 143 | 140 | - | - | - |
| Universal columns | ||||||
| 152 | 65 (24) | 92 | 90 | - | - | - |
| 203 | 75 (24) | 143 | 140 | - | - | - |
| 254 | 87 (24) | 194 | 140 | - | - | - |
| 305 | 100 (24) | 245 | 140 | 120 (24) | 60 (24) | 240 (24) |
| 368 | 88 (24) | 308 | 140 | 140 (24) | 75 (24) | 290 (24) |
| 406 | 120 (24) | 346 | 140 | 140 (24) | 75 (24) | 290 (24) |
| Universal Beams | ||||||
| 102 | 50 (16) | 62 | 54 | - | - | - |
| 127 | 62(20) | 77 | 70 | - | - | - |
| 133 | 57 (20) | 83 | 70 | - | - | - |
| 140 | 69 (24) | 80 | 70 | - | - | - |
| 146 | 64 (24) | 86 | 70 | - | - | - |
| 152 | 73 (24) | 92 | 90 | - | - | - |
| 165 | 67 (24) | 105 | 90 | - | - | - |
| 171 | 72 (24) | 111 | 90 | - | - | - |
| 178 | 72 (24) | 118 | 90 | - | - | - |
| 191 | 74 (24) | 131 | 90 | - | - | - |
| 210 | 80 (24) | 150 | 140 | - | - | - |
| 229 | 80 (24) | 169 | 140 | - | - | - |
| 254 | 87 (24) | 194 | 140 | - | - | - |
| 267 | 91(24) | 207 | 140 | 90(20) | 50 (20) | 190 (20) |
| 292 | 92(24) | 232 | 140 | 100 (24) | 60 (24) | 220 (24) |
| 305 | 100 (24) | 245 | 140 | 120 (24) | 60 (24) | 240 (24) |
| 419 | 112(24) | 359 | 140 | 140 (24) | 75 (24) | 290 (24) |
The back mark is the distance from the back of a section (such as a channel or angle) to the centre of a bolt hole.
Edge distance ensures the material around the hole does not fail due to tearing or shear.
They are chosen based on accessibility, structural requirements, and minimum edge distance standards.
These values are typical engineering recommendations but should be checked against relevant design codes.