Bearing - Driving Side Roller Bearing KSS Mk1, KTS, MAC, MOV, MSS & Post 1951 Alloy Head MAC - RHP (Ransome Hoffman & Pollard) UK Made and Boxed - SEE K87 for UK Made Ball Bearing Type
For Mk2 KSS use M87 the Double Roller Drive Side Bearing with 1 thou per inch taper - These are Metric Bearings with a 50mm OD and a 21.86mm bore (this is as close as we can measure without a Bore Gauge)