Code 332, 250, 215 ??
Code classifications are referring to different rail types. Rails as different in height, base width, and head width. I found data from the 1939 American Railway Engineering Association standards for rail sizes and converted it to the equivalent scale sizes. If you know the weight of the prototypical rail then you can find the appropriate code in the table below. For example, the chart shows 140 pound rail in G scale to be 0.311, and the closest 'code' rail would be code 332. The table contains also the base widths and the head widths for your reference.
When do you look into the G-scale or #1 table? We refer to #1 when we are modeling 1:32 which is standard gauge (1435mm or 4' 8 1/2") in the prototype. G-scale is more appropriate for 1:22.5 or 1:20.5 which reflect narrow gauge (1000mm or 3").
Now we need the weight. In the US, rail weight varies from 80-90 lb/yd (pounds/yard) in small yards to 100-110 lb/yd on light duty track and between 130 and 141 lbs on heavy duty track. Rail of 141 lbs is the new main line standard. The infrastructure owning company in the UK (Railtrack), has adopted UIC60 rail (which weighs 60 kg/m or 125 lb/yd) as its standard for high speed lines. The present standard is equivalent to the UIC 54 rail, which weighs about 113 lbs/yd or 54 kg/m.
So know we can figure out the correct code type. If we assume heavy duty track we would find that in 1:22.5 code 332 is just fine. However, most likely heavy duty would run on standard gauge and 45 mm is only standard gauge in 1:32 (or to a lesser degree 1:29 the obscure scale of Aristocraft and USA Trains (and of course all standard gauge locomotives from LGB). So code 250 would be probably a better choice for 1:29 and code 215 for 1:32. With that said our experience for proper outdoor operation shows us that we are better off with code 332, which has less problems with stone and dirt movement caused by weather, animals, or us and our kids. We recommend to reserve code 250 and 215 for indoor layouts.