Typical application is four sheaves in the masthead for either internal or external halyards. Four sheaves accommodate two external halyards (two sheaves for the main and two for the jib). When used with internal halyards, four sheaves will accommodate two jib halyards, a main halyard, and perhaps an internal boom topping lift if desired.

Sheaves will fit the mastheads of the Catalina 25, Catalina 27 and Catalina 28s.

• Outside diameter: 1-7/8"
• Inside diameter: 5/16"
• Width: 0.413"
• Line diameter: 5/16"

Will not fit Catalina 27s with hull numbers in the following ranges: 1421-1450, 2465-2549, 3101-3150, 3950-3999, 4701-4725, 5042-5051, and 5140-5149. These boats were not built in California and used a different mast. There may be other ranges as well that we have not discovered yet.