Have had Plenty of ROBBINS Belts off of Dearborn Cars and San Jose. All of the 68-69 Belts we have had in the past few years were Robbins Jr. Mostly have noticed Hamill on 1970-Later cars. I do not think it was a Plant Difference, although NJ cars are few and far between here. I would lean more towards them each making certain types of belts, but can not positively verify that. I hope this helps at least a little bit. Andrew.