This allows you to plug up holes in desks with wires running through them. The hole for the bolt ut is 1 8th of an inch, the tube's OD is of 33mm (shrinks to about 32.5mm), which is a hair above 1 and a quarter inch. Hole saws tend to shave slightly more than what they indicate (at least mine do, maybe they are just not very good). This is a very snug fit. I do recommend cleaning the bolt hole by drilling through both peices at the same time, that way they stay aligned.