Ted,
The harkens are 75mm carbo blocks. #2665 is the triple/becket 3639lb SWL ,#2660 is the single 1213lb SWL, #2662 is the double 2426lb SWL.
I still am hesitant to load up these all plastic blocks but the Triple has a break strength of 10,000lbs! The lewmars look stronger but I think its...