Does anyone happen to know what are the maximum string gauges useable – without modification – with (a) the standard bakelite saddle, (b) the Dipshot Rickenbacker Pre-2020 Replacement Bridge 5RK400BC Brass/Chrome?

Many thanks in advance

1) Rickenbacker has never used bakelite saddles. Do you mean the die-cast zinc saddles?
2) We do not discuss aftermarket parts. Go to rickresource.com for that.
3) Why? Is a standard 40-100 or 45-105 set insufficient? Anything larger than this will require nut and bridge groove widening. Do you want to do that? We all recommend against that due to the difficulty of cutting a new nut and bridge saddles if you want to return to a 40 or 45 string set.

The heaviest gauge strings I ever used on a Rick were Thomastik-Infeld Powerbass (.047 - .068 - .080 - .107), but I've used sets up to .055 - .110 on other 4-strings.

Maybe I'd then better have my luthier install another nut.

Nevertheless, thanks for the info.