[George16]

The narrower diameter is for use with an e-clip just like the stock nitro setup. However, you can also a screw at the end of the shaft with 1/8 scale clutch bells (just like in the picture you posted) because 1/8 cb are wider than the stock revo cb. I have my revo (3.3 engine) setup with an e-clip while my tmaxx (OS .18TZ engine) uses a screw at the end of the shaft to accommodate the wider kyosho cb (or other 1/8 cb for that matter) I'm using.