Maybe this page should not be necessary, but a few people have been asking questions about the fasteners securing the disc brake rotors to the bearing hub. Notice items 22 and 27 in the illustration below. Early in MGA 1600 production these were double threaded studs, later changed to headed bolts with splined neck. This illustration is from the MGA 1600 Service Parts List.

- Item 22 - BTB104 - is a stud, for disc wheels only. - Fin. (C) 69504 - Item 27 - BTB104 - is a stud, for wire wheels only. - Fin. (C) 70275 - Same stud, first hub assembly at different change-over time. - Item 22 - BTB145 - is a bolt, for disc wheels only. - Com. (C) 69505 - Item 27 - BTB145 - is a bolt, for wire wheels only. - Com. (C) 70276 - Same bolt, second hub assembly at different change-over time.

That is, the stud changed to a bolt with a hex head, but the washers and nuts are always behind the rotor. So you have to remove the bearing hub to change a rotor. The hub change was only for the difference between stud or bolt. I suppose at the time someone thought the bolt assembly was cheaper than the stud assembly.

My best guess so far is that the early part maybe a press-fit stud with knurled neck, similar to a lug nut stud for bolt-on wheels. I hope to document this stud when information may be available.

Notice the later replacement hex head bolt is also a special drawing number. This may be due to the need for a special close fit (and non-standard length) for the pilot diameter on the shank of the bolt. That is, it may have shorter threads than normal for a bolt of the designated length. I would like to document the dimensions of this bolt as well.

BTB104 Stud.

BTB145 Bolt.