they hammer out and have a shoulder to bit the housing just like a wheel stud in an axle flange
get them from moser for a set cheap,come in packs of 10
did mine when i set it up,I used a small stack of washers and the air ratchet to pull them in all the way first then droped the chunk in.
the ones for the backing plates have a T shape thats flat on one side to fit in the end cap on axle tub..i would not use that on the punkin myself as its not were it goes
they can be had cheap from moser also
may try Doctor Diff here on the board for them
dont forget to doll it up for your bro either