See also the general article on Fan mounts Ken Chorney says:
Just wanted to add an alternative supplier for replacement fan mounts for the Tektronix 545 oscilloscope fan. Digi-Key currently stocks two part numbers which fit and work perfectly: RPC1597-ND and EAR1345-ND. Both are 1/2" length (same as original) and both have 8-32 male threaded ends (same as original). Both are slightly smaller in diameter (0.4" vs. the 0.5" originals) but this does not affect their fit at all and likely does not affect their function appreciably. I have installed three of the RPC1597-ND standoffs in my 545 and they fit and work perfectly.