300mm diameter. A have 2 different designs. Uses 8mm threated rods and m8 nuts. Can hold up to 5kg material. Used spool holders fit on 30mm al square profile.U need 2 pieces of "priruba", 2 pieces of ball bearings 608, 10pcs of clanek a, and 10ps of clanek b, 1pc 290mm rod, 10pcs 120mm rods, 10pcs 160mm rods, 42pcs of standard m8 nuts, 32pcs of m8 self locking nuts. Holes on both sides works as places for fixing filament and inserting small pieces of flexible filament working as "break" (see picture). Older version with less holes need to be left and right side mounted rotated by 39 degree (for better "break" distribution.