Just had a look at their website. The 44100B is for a different type of leg, the SX.
The 42100B suits the legs you need for the Disco. I have LR rails which they recommend the RLT legs for, but I now use the RLTP legs which make the rack sit lower.
The other advantage of the RLTP legs is they have 2 mounting screws instead of one. I had problems with the RLT legs coming loose on my Flinders trip last year.
Cheers,
Jon

