These sheaves were used as boom end sheaves at both the inboard and outboard ends of the boom. Below is a Inventory of the usage:
• (4) per Catalina 400 boom with F760-E in-mast furling mast and F810 boom
• (6) per Catalina 42 Mk II boom with non-furling F740 mast and F810 boom

• Outside diameter: 85mm (~3-11/32")
• Width: 20mm (~7/8")
• Requires plastic bushing (included): ID: 12mm (~1/2")

Since these spars are French, all of their products are metric. The fractional dimensions provided are the nearest equivalents.