Many mechanical end connections have threads. If the threads on two parts don’t have the identical diameter and pitch, you can’t connect them. If dealing with a port fitting, the first step towards thread identification is to determine whether the thread is parallel or tapered. Threads have peaks called crests and valleys called roots. The part in between the crest and the root is called the flank. The first thing to check is whether the crests are all of the same diameter. Use calipers and measure the first, fourth and last crests. If the measurements are the same, you have straight threads. If you get three different measurements, then you have tapered threads.
A seal must be used for all parallel fittings in port application, with the exception of Cutting Face fittings, however these are fairly rare. It is important to note that BSPT (British Standard Pipe – Tapered) can seal into a parallel BSP port, and Metric Tapered threads are capable of sealing into a parallel Metric port.
his first step will help you eliminate a number of possible thread types, as well as possibly reveal the method of sealing. For a parallel thread in port application, the fitting will usually seal at the top of the thread by means of an O-ring or seal. A sealant is not required or recommended on straight threads. Depending on the application and materials, thread lubricant may be used. With a tapered thread, the fitting typically seals via metal-to-metal wedging of the threads. But they always need a sealant to seal system fluids and reduce the potential for galling of the threads.
Below are some examples of tapered and parallel threads that seal in the examples given:
QC Hydraulics is one of leading professional manufacturers of stainless steel hydraulic fittings, with over 20 years production experience, we can provide all popular threads fittings in the market. If you have any trouble of choosing correct hydraulic fittings, please contact our team for professional advice and assistance.