Color classification: [No wheel] No. 1 round high-grade gray / inner diameter 16.3 [high load-bearing / anti-skid silent wheel] No. 2 round 4-wheel high-grade gray / inner diameter 19.3cm [high load-bearing / anti-skid silent wheel] No. 3 round 4 wheel High-grade gray/inner diameter 22.3cm [high load-bearing/anti-slip silent wheel] No. 4 round 4-wheel high-grade gray/inner diameter 25.3cm [high load-bearing/anti-slip silent wheel] No. 5 round 4-wheel high-grade gray/inner diameter 28.3cm [high load-bearing/ Anti-slip silent wheel] No. 6 round 5-wheel high-grade gray/inner diameter 31.3cm [High load-bearing/anti-slip silent wheel] No. 7 round 5-wheel high-grade gray/inner diameter 34.3cm [High load-bearing/anti-skid silent wheel] No. 8 round 7 wheel High-grade gray/inner diameter 37.3cm [High load-bearing/anti-slip silent wheel] No. 9 round 7-wheel high-grade gray/inner diameter 40.3cm [wheelless model] No. 1 round off-white/inner diameter 16.3cm [high load-bearing/anti-slip silent wheel] 2 No. 3 round 4-wheel off-white/inner diameter 19.3cm [High load-bearing/non-slip silent wheel] No. 3 round 4-wheel off-white/inner diameter 22.3cm [High load-bearing/anti-slip silent wheel] No. 4 round 4 wheel off-white/inner diameter 25.3 cm [High load-bearing/non-slip silent wheels] No. 5 round 4 wheels off-white/inner diameter 28.3cm [High load-bearing/anti-slip silent wheels] No. 6 round 5 wheels off-white/inner diameter 31.3cm [High load-bearing/anti-slip silent wheels] 7 No. 8 round 5-wheel off-white/inner diameter 34.3cm [High load-bearing/non-slip silent wheel] No. 8 round 7-wheel off-white/inner diameter 37.3cm [High load-bearing/anti-slip silent wheel] No. 9 round 7 wheel off-white/inner diameter 40.3 cm