Hot tub filter thread terminology can be confusing, but the simple explanation is:
- MPT stands for male pipe thread and is a finer thread
- SAE threads are coarse thread (shown here on the left)
The longer explanation is more complicated, but for hot tub filter applications, there are mainly either fine threads or coarse threads (if the filter has a threaded connector at all).
More Details About Male Filter Thread Sizes
In a wider sense, MPT is the same as NPT which stands for National Pipe Thread Taper. That is the United States standard for tapered threads on fittings and pipes. The connector on the right is an MPT spa filter connector. (MPT = male pipe thread)
A non-threaded connector would be referred to as a “slip fitting” or SLP.
To make matters a little more confusing, the same threads may be offered as a female connector instead of the male connector. (FPT = female pipe thread). (For a full explanation, you can read the Wikipedia article.)
Female Threaded Connector Measurements (SAE-F)
Note the female threaded socket size is listed as a nominal pipe thread size of 1-1/2″, but that is not the actual measurement of the inside diameter. This 1-1/2″ coarse threaded socket actually measures about 1-7/8″ inside diameter (I.D.) for your reference.
Identifying Filter Thread Size
Threads can be identified by visual inspection or even by a caliper tool. Once you know the type of thread your hot tub filter has, you won’t need to know this again. Just be sure to order the correct filter thread type (fine = MPT or coarse = SAE) and whether the connector is a male connector or a female connector.
Pleatco Removable Threaded Adapter
If your spa had an old Pleatco filter in it, chances are it had a removable threaded adapter fitting. These little male pipe threaded fittings fit into a slightly smaller than 2″ diameter opening. Since most new replacement filters have the threaded connector on them, you won’t need that adapter but should remove it if it is still inside.er
Spa Filter Thread Sizes
Spa filter threads usually come in either 1 1/2″ or 2″ fine (MPT) or 1 1/2″ or 2″ coarse (SAE) threads. The actual diameter of the threaded connector is actually 1/4″ larger than that specified when measured. So the 1 1/2″ male pipe thread connector would actually be 1 3/4″ wide.
Some Pleatco filters have a removable threaded connector which can be unscrewed, while other filter brands and types have the connector molded to the filter end cap.
Find your filter by entering the filter model in the search box above or get the model number by measuring your old filter and search by filter dimensions.
Learn more about Pleatco hot tub filters.
More about Master Deluxe hot tub filters.
Once you identify the filter model number, you won’t have to measure your filter anymore, simply reorder with the filter model number.