This is an elevated track support designed for O/O27 gauge trains such as Lionel Trains or MTH. There are two screw holes in the top, at least one should line up with tubular track, I don't have Fastrack or anything like it to test that. There's also one hole on the bottom to insert a screw from under your layout into the support if you wish. Supports are designed to be ½" thick, 7.25" tall and 4.5" across the top where the track or roadbed would go.  I would recommend placing one roughly every 10" of track.