| Inches | Millimetres | |
| 1 1/2" | = | 38mm |
| 1 3/4" | = | 48mm |
| 2" | = | 53mm |
| 2 1/4" | = | 58mm |
| 2 1/2" | = | 63mm |
| 2 3/4" | = | 68mm |
| 3" | = | 78mm |
| 3 1/2" | = | 88mm |
| 4" |
= | 103mm |
| 5" | = | 128mm |
| 6" | = | 153mm |
| 7" | = | 177mm |
| 9" | = | 228mm |
| 10" | = | 254mm |
| 12" | = | 305mm |
| 15" | = | 381mm |
| 16" | = | 406mm |
| 18" | = | 457mm |