What is the difference?

Hi Folks, new guy here. Just have a question regarding rear master cylinders. Wile looking for a master cylinder housing I came across what appears to be the same part with two different part numbers. They are 99-9918S & 99-7027. Are they the same or interchangeable?

Welcome to the forum, SpacecoastDale.

99-7027 is the master cylinder barrel.

99-9918 is the master cylinder barrel assembly (barrel, piston, seals, etc.) S = stainless steel.

Thank you for the help about the difference, I was hoping it would be something simple like that. I have an assembly on order (from the UK), we'll see how long it takes to arrive.