For your consideration is these nice Harken blocks.
One is a micro block, lightweight carbon black Delrin ball bearings, small size ideal for inside spars. Specs: Sheave Diameter-7/8" (22mm)
Max Line Size-1/4" (6mm)
Breaking Strength-1200 lbs (544kg)
Shackle Pin Dia-3/16" (5mm)
I cant give exact specs on the other larger block. Also has ball bearings, Stainless and black carbon sideplates, shackle and pin.
Both have never been used and are in great condition.
Thanks for looking and take care