| Identification of chokes | |||||
| International designation | Leed shot chokes, mm | Steel shot chokes, mm | |||
| Gauges 12, 16, 20 | Gauge 28 | Gauge .410 | Gauge 12 | ||
| Cylinder | C | 0.0 | 0.0 | 0.0 | -0.2 (bell) |
| Improved cylinder | IC | 0.25 | 0.15 | 0,12 | -0.1 (bell) |
| Modified | M | 0.5 | 0.25 | 0,25 | 0.1 |
| Improved modified | IM | 0.75 | 0.4 | 0,38 | 0.2 |
| Full | F | 1.0 | 0.6 | 0,5 | 0.4 |
| Extra full | XF | 1.25 | - | 0,8 | 0.52 |