Hypo tubing gauge guide for model airplane guns.
7.92mm/.30cal : 1/48th = 29 gauge - 1/32nd
= 28 gauge
13mm/.50cal : 1/48th = 28 gauge - 1/32nd = 23 gauge
20mm
: 1/48th = 23 gauge - 1/32nd = 20 gauge
30mm
: 1/48th = 20 gauge - 1/32nd = 18 gauge