What is the difference between this Shimano BB-UN50 and the BB-UN55 ? The former is hard to find for sale, the latter seems to be found everywhere : r/bikewrench
アスクル】 ハート光学 老眼鏡 +2.5 UN55(直送品) 通販 - ASKUL(公式)
Qoo10] BB-UN55 73BSA 113mm
Shimano UN55 Staffa inferiore cuscinetto BB 68 mm 127 mm asse conico quadrato | eBay