We believe this block was used on early boats before Catalina Yachts had one of their fabricators build a version exclusively for them. It has a unique six hole mounting hole pattern. Later blocks have a four hole pattern. The two mounting hole patterns overlap, making it impossible for this early use block and the later production block to be used interchangeably.

It has been years since this part was used and we only have an occasional request for it, therefore we do not carry many in stock. But they are available, so if you need one give us a call. We may have one or two on the shelf. If not and you are patient we can still get more for you.

Minimum mast mounting hole size:
• Height: 54mm (2-1/8")
• Width: 19mm (3/4")

Fastener hole spacing, center to center:
• Vertical: 20mm (3/4")
• Side to side: 32mm (1-1/4")

Fastener diameter:
• Mounting holes cleared for 3/16" fastener (stainless pop rivets are ideal)

Mounting plane overall dimensions:
• Height: 54mm (2-1/8")
• Width 43mm (1-11/16")

• Sheave diameter: 40mm (original was 38mm)
• Maximum line size (as reported by manufacturer): 3/8"

1) Only the metric dimensions are accurate. The imperial dimensions are the closest equivalent.

2) Recently we learned that the manufacturer of this block has changed its dimensions as well! Looking at the current block's dimensions (detailed above) you will notice that the width of the mounting hole pattern is about 1/8" (1/16" per side) farther apart than those on your original block. This is because a slightly wider sheave, suitable for 5/16" line, is now used.

It will be necessary to ream the holes on the mast 1/16" wider to fit this new block. Using a pop rivet in place of the original self tapping screws would likely be adequate. If you desire extra strength, luckily the blocks are not very far up the mast. If desired you can reach up into the mast and add small backing washers behind either pop rivets or through bolts and nuts.