We now have spar spacers back in stock in several widths.
1.438 (Vans suggestion) although most spar stubs measure around 1.444.
making a hole smaller than what you intend to put in it is asking for trouble.
Generally, I recommend 1.445" spacers.
These are designed for RV 7,8 & 9, but may fit others. They have a 7/16 ID.
http://BullerEnt.com/SparSpacer.htm
