Retaining nut for TFL catamaran 110mm drive pn# tfl-503b78a

Retaining nut for TFL catamaran 110mm drive pn# tfl-503b78a. See picture 1, the item is circled in RED. 
Picture 2 shows the tfl-503b78A drives that this will fit.

Specs: 
(1) Color silver
(1) Nut per package
This works with part numbers ose-80108, tfl-503b78, tfl-503b78-A