Fits the Advanced Telescope Systems Portable Pier. Advanced Telescope Systems has built two slightly different versions of this. Current production has a 3/8"-16 threaded hole in the bottom of each leg. This caster set screws into those threaded holes.
The Deluxe model uses a 4" wheel, not the 3" wheel common to the other Deluxe models.
Note: if you have the hard rubber footpads already installed on your Advanced Telescope Systems Portable Pier, you do not need the spacer block shown in this picture, because the hard rubber footpad already performs this function:
ScopeRoller ATSPP Deluxe With Spacer Block