This particular shackle, #Z4013 is specific to the gooseneck used aboard the Catalina 320 (both non-furling and furling mast), as well as the Catalina 34 and Catalina 36 (in-mast furling rig only).
Bow shackles round shape allows for use with line, chain or multiple items; a typical application is dinghy lifting bridles. The photo above provides a relative size comparison to help you choose. Click one of the links in the "Other Sizes" tab to choose a different size shackle. Click "Order Now!" to purchase the part number specified for this shackle below. See "May we also suggest" at the bottom to select other types of shackles.
Specifications for this Shackle #Z4031:
• Nominal size: 5/16"
• Pin diameter (A):
8mm / 0.312"
• Outside length (B): 68 mm / 2.687"
• Inside length (C): 42 mm / 1.656"
• Inside width (D): 22 mm / 0.859"
• Safety wire hole: Yes
• Construction: Forged
• Captive pin: No
• Material: Type 316 stainless steel