This is a chair for holding #4 (1/2 inch) rebar for a 4" thick concrete slab. The chair has upper and lower clips to hold crossing pieces of rebar, centered 2" above the ground. The chair keeps the rebar grid in the proper position as concrete is poured.
Print this using HIPS to keep the cost low. I used 0.28mm layer height with my 0.35mm extruder nozzle.