1:87 scale
3.5mm = 1 foot
track gauge is 0.650" or 16.5 mm

Rail Sizes

Rail Size	Scale Size	Proto Size
Code 55	4.78"	75 lb
Code 70	6.09"	110 lb
Code 83	7.22"	132 lb
Code 100	8.7"	over 140 lb

HO Scale Track Dimensions

Dimension	Target	Plus	Minus
Guage at frog	0.651	0.010	.002
Check Gauge	0.607	0.007	0.002
Flangeway	0.048	0.002	0.008
Points	0.588	0.002	0.004
Flangeway Depth (min)	0.028	0	0

From NMRA S-3.2 Scale Track, Standard Scale



HOe - HO scale on N scale track. 9 mm gauge = 30.86" gauge. Also known in USA as HOn30