This is a set of replacement shocks for Bowflex Treadclimbers models TC-1000, TC-3000, and TC-5000 version one. To determine which version your machine is, go to the front of the machine and unlock your treadles. Push down on one of the treadles to it's lowest position. If the treadle raises back to the resting position and the opposit treadle does nothing, you have the version 2. If the treadle stays at the lowest position and the opposite treadle raises, then you have the version 1 treadclimber.