It is all same diameter 36CM for all sizes. It is very strong.It is not easy breaking. Spec:4lb,6lb.8lb,10lb,12lb,14lb,16lb Medicine ball:1-It is all same diameter 36cm for all sizes.2-Spec:4lb,6lb.8lb,10lb,12lb,14lb,16lb,18lb,20lb,25lb,3kg,4kg...9kg,3-It is very strong PVC leather and not easy to break.4-Colour: balck+ green/red/yellow/purple.....5-carton box size:72cm*36cm*36cm