I looked up the
gun, it's an 18 gauge gun which will take 18 gauge brad nails from 20 to 50mm. What are the nails you have bought?
Nails/brads? It's terminology. The trade in the UK generally refer to the nail guns by work type, e.g. "first fix nail gun", "second fix nail gun" and sometimes "pinner". Brad is an American term which has crept in to cause confusion
1st fix nails - nails from about 2.4 to 3.3mm shank thickness with a full round head, an offset full head or a D-shaped (clipped) head, These can be hand driven if needs be and are used for structural framing, sub-flooring, etc. Most 1st fix nailers are desgned to use paper or plastic collated nails, 2.8 to 3.3mm diameter x 50 to 90mm shank length
2nd fix nails - nails (or pins) with three specific sizes, 15 gauge, 16 gauge and 18 gauge. 15 gauge nails have a round body and a fully formed small head - I use a gun which drives 15 gauge nails, but they are rare in the UK. 16 gauge nails, which are the standard for installing architraves, skirtings, etc are flat strip nails and come in lengths from 25 to 64mm. 18 gauge nails, which are more for attaching small to medium size mouldings, etc are again a flat strip nail with lengths 16 to 50mm. Americans refer to 18 gauge pins as "brads"
Smaller pinners - some manufacturers make a fine, headless pin in 20 to 23 gauge. Lengths are normally restricted to 35 or 40mm max length. These very fine nails are used specifically to fix beadings to furniture and similar tasks because the holes made is near invisible
The guns are referred to as nailers or nail guns in sizes from 18 gauge up to 3.3mm; 15 gauge and smaller (down to 23 gauge) are also referred to as pinners
"Gauge" refers to AWG or American Wire Gauge and describes the size of the shank. The higher the gauge, the smaller the nail or pin