Coarse Contractor Thread & Fine Standard Thread

There are two different common threads widely used on abrasive blast nozzles and blast nozzle holders. We generally called them Coarse Contractor Thread and Fine Standard Thread.

Then what’s the difference between the coarse thread and fine thread? Let’s learn about them.

The coarse contractor thread is 50mm Industry-standard thread at 4½ threads per inch (TPI) (114mm), so it is also called 2-inch threads sometimes. It is like a wood screw. There’s a lot of room between the threads and they look much bigger.

Fine thread is called the National Standard Free-Fitting Straight Mechanical Pipe Thread (NPSM). It is the Industry standard straight thread used widely in North America, which looks like a machine screw. Two sizes of fine thread are widely used in blast nozzles: 1-1/4″ thread and 3/4”-14 thread.

The difference between the Contractor thread and the standard thread is quite obvious. The size and the distance between two threads of coarse Contractor thread are much bigger than fine thread. We can see them from the photo as below.

For Coarse Contractor Thread vs. Fine Standard Thread, we wouldn’t say one is better than the other one. Clemco and Contracor offer the 50mm coarse thread as standard and to their credit, we here at BSTEC like to use the contractor thread as the main thread type for blast nozzles and holders. There’s less chance of cross-threading or mangling up the threads because they are much bigger and it is much easier to install. When blasting with finer media, you won’t have the issue to get the media stuck.

For 1-1/4″ Fine Thread, it is more popular than the contractor thread in North America for its term Standard. When you buy an abrasive blaster from Schmidt, Empire, Dustless Blasting, Marco, and others, the first nozzle that comes with that machine is going to be 1-1/4″ fine thread. That’s why it’s standard in the North American market. The fine thread takes a longer time than coarse thread when installation, and you may get the media stuck when you use very fine media. But the fine thread has better strength on tensile and shear performance than a coarse thread for its thread pitch.

Anyway, whatever thread type you prefer, make sure your nozzle and your nozzle coupling match threads when placing your order. BSTEC mainly carries the 50mm Contractor thread and 1-1/4″ fine thread. We also have 3/4″ threads for those smaller units and blast cabinets.