These bogies sub frames are of the rigid type, designed to accept a 26mm axle length (Alan Gibson, Ultrascale etc) wheels. The purpose of the sub frames is to hold the bearings and wheels in place, and to accept a cosmetic bogie side frame on the outside.

The design of the sub frame is such that the minimum of material is visible outside of the bogie casting (where strength allows). Therefore each bogie sub frame type is designed for a specific bogie type only. The subframes allow a quick and easy way to re-bogie coaches (such as MK 1s to B4 or Commonwealth type) as well as to change the gauge on Lima coaches (e.g. OO to S4). Not suitable for short length Lima axles.

Each type contains one pair of bogie sub frames for one vehicle. Top hat bearings and wheels are required to complete.