fooyabt -  fessyFOO's Yet Another Belt Tensioner
Belt Tensioner for Tronxy X1  and other that use the v-slot extruded aluminum rails.
have STL's in a few sizes specified by their range of travel:  10mm, 15mm, and 20mm.   filenames vary by rNN where NN is the range of travel.  the nut is the same for all of them.
15mm  one is probably sufficient.   I like the 10mm because I wanted things as small as possible.
the puller and the case are designed to be printed upside down, no supports  the stl files should be that way already.
caveat emptor:  using this on the y axis of the tronxy x1, it still has a 4mm flange.  which keeps the bed from getting  all the way to the edge.  if you were using that 4mm you will miss them.   at some point I hope to redesign the part to handle that.  (adding slot for the wheel, assuming it still has enough support. )
see youtube video  for demonstration.
openscad source is available on github