A piece of common 1" water pipe (galvanized or black iron, seam weld doesn't matter) from any local hardware store will slide right over a 1" gokart axle with a fair enough fit, same for 3/4" pipe to 3'4" axle, and make an ideal custom U-Cut-It spacer of any length for the INSIDE of FLANGED bearings. They also are great for entire axle-length spacers from the inside of one wheel's inside bearing all the way to the other wheel's inside bearing, with the appropriate spacing cut for sprockets, brakes, more bearings, etc. Backing up here, if your axle bearings don't have flanges that allow you to tighten down all the way, or as with most bearings require a fine-thread thin nylock nut that allows a tightening to a certain point but won't back off because of the nylon insert, there's other options. With enough threads available, you can have a fine-thread nut on the inside of the hub for tightening a stretch of pipe spacers and components down tight (excluding other bearings), and use 2 fine thread nuts torqued down tight together (in place of a thin nylock nut) outside of the hubs for the hubs' bearing tension.
