The National Model Railroad Association (NMRA) has Standards and Recommended Practices for various things for Model Railroads. These range from track spacing, wheel profiles, module specifications, and Car Weight. This page is going t focus on Wheel Specifications.

S-4.2 Wheel Standard Scales establishes a set of standards for Wheels in different scales. The following graphic show the O scale information from the PDF file.

The following is a chart of the different manufactures wheels, wheelsets and trucks that I have had the chance to measure. This does not mean that all of a manufacture’s product as listed here is either in or out of NMRA specification. It just means the products I had the chance to measure were as written below.

Numbers in Black Type are within the NMRA Standards.
Numbers in Red Type are NOT WITHIN NMRA Standards.

Last Updated 10/10/2022

Manufacturer / Type	K 1.177 1.171 1.179	B 1.138 1.132 1.140	N .145 0.143 0.147	D .036 0.034 0.038	T .039 0.037 0.041
American Scale Models Arch Bar Caboose Trucks	1.189	1.146	0.147	0.039	0.038
Atlas-O EMD F3 wheelsets	1.179	1.122	0.175	0.040	0.047
Intermountain 33″ metal wheelsets	1.182	1.125	0.162	0.046	0.056
Intermountain Plastic	1.170	1.140	0.138	0.035	0.036
PRB 50 Ton truck Under SFRD Reefer	1.167	1.116	0.158	0.037	0.038
PSC 33inch	1.178	1.128	0.147	0.044	0.043
P&D EMD Drive	1.182	1.127	0.177	0.049	0.041
Protocraft 50 ton Bettendorf	1.177	1.123	0.157	0.045	0.046
NWSL .145 RC GP-9	1.182	1.138	0.153	0.037	0.053
NWSL .145 Atlas SW-9	1.195	1.142	0.149	0.035	0.042
Yoder 50 ton Truck	1.177	1.120	0.160	0.043	0.052
Yoder Andrews Truck	1.189	1.122	0.147	0.042	0.054
Yoder USRA 70 Ton Truck	1.172	1.125	0.158	0.042	0.040
Yoder Crown 70 Ton Truck	1.165	1.120	0.149	0.045	0.046
Yoder National B-1 Truck	1.181	1.125	0.149	0.041	0.054
MTH 2-rail Truck	1.171	1.105	0.175	0.045	0.052
Overland Taylor Caboose truck	1.167	1.117	0.177	0.045	0.046
Weaver Diecast Truck on B&O M-53	1.187	1.131	0.177	0.062	0.052
Weaver Diecast Truck on Milwaukee Car	1.196	1.140	0.176	0.054	0.056