Measuring HO wheel size for Athearn blue box box cars etc.

I am building a train table for some kids at Urban Ministries in Birmingham. I have been an O scaler for 50 yrs but now have a bunch of HO trains and transformers and we are building a 4 x 8 layout. When I measure the plastic wheels on these old kits, they measure .436” outside dia of the flange. When I look that up, it shows a 38” wheel. In reading at various sites I see where everyone says that the Athearn blue box kits should use 33” and 36” wheels. I don’t need to waste money purchasing the wrong items….can someone give me some guidance, please??