Plain and simple is the name of the game for these guys. They have a simple construction with the least amount of moving parts you can find in a block. Generally they made of a plastic or metal sheave (the wheel thing) rolling on a metal pin or bushing. In some instances, they were made of Bakelite (1940’s or so) or even wood (think Mayflower).
Like most things, manufacturers have made improvements over the years. Some have added low friction metal sleeve bearings and side-races of ball bearings. This design reduces friction between the cheek and wheel when the block has an uneven load, but does not take any of the actual load.
New designs of blocks were developed such as the modern ball bearing block (Harken 1967) or later, roller bearing blocks. These advances in design reduce friction and are much easier to adjust under high load.
Despite this, plain bearing blocks still have their place in the world of sailing. For one, they have the highest strength-to-price ratio of any block we sell making them extremely cost effective.
They are a good, all-purpose blocks – a jack of all trades if you will. They don’t run as smooth as a ball bearing block but they are stronger. They may not adjust as easily under high load as a roller bearing block, but they are still less expensive.
Are they always the best block for the job? No, but they can be used in most any application. For these reasons, plain bearing blocks are often used as Original Equipment Manufacturer (OEM) on many boats.
Plain bearing blocks are perfect for high, static loads. Because of this, they can be are especially well suited for halyard turning blocks, runner or backstay blocks, and vangs.