maxi-model
UK/US/ROW steam narrow gauge railways 1:1

I think in the US there is quite a fit with 45 mm track gauge and what constitutes their main areas of interest - 1:29/32 mainline stuff and 1:20.3 3ft narrow gauge - and the product ranges have grown up to reflect this.
What I think really defines "G" is the use of the robust 45 mm gauge code 332 (rail height in thou' of an inch) rail dimensions and systems. The plethora of stock that run on these compatible track systems, irrespective of scale, all have wheels/flanges and geometries to take advantage of the very generous rail depth available. Ok, yes there is Peco G45 which is code 250. Max.
What I think really defines "G" is the use of the robust 45 mm gauge code 332 (rail height in thou' of an inch) rail dimensions and systems. The plethora of stock that run on these compatible track systems, irrespective of scale, all have wheels/flanges and geometries to take advantage of the very generous rail depth available. Ok, yes there is Peco G45 which is code 250. Max.