... at 50mm H4 Heavy duty type double ball bearing swivel caster wheel Heavy Duty Caster /Four Size available (4'',5'',6'',8'')[Model ... 3.Caster material: PU wheel tyre with pp core .this wheel core is adopted new latch technical.blue zinc plated, Top plate swivel ... double ball bearing, 5.8mm thickness pressed steel .4.Top plate swivel brake type ,fixed type ,threaded stem type,Bolt hole type ...