In B&O files located in various places, there are a number of Bills of Materials for B&O freight car orders existing for study. These are jaw droppingly insightful.

B&O ( ..... and I assume other railroads ..... ) spread the business around. A single 1000 boxcar order can have three different brake beams, two different running boards, two different truck sideframe castings, and three different power brake wheels. In these bills of materials, the car series' were called out, which car numbers had what equipment.

I used to make generalizations about freight car hardware from several photos, but the B&O experience shows equipment varies greatly, even within the same order.

This perspective makes freight car databases, either informal or comprehensive, something of a fool's errand.