Learn to identify threads

Posted by Marek Bobik on Tue, Apr 13, 2010 @ 12:04 PM
Marek Bobik

Identifying the thread of a fitting is an important step to identify a Parker (or any other manufacturer's) fitting part number. However, the information below is general in nature and applies to any threads in any situation, such as threads on bolts, ports or machined parts.

Two different thread styles are parallel threads and tapered threads. Parallel threads only serve the function of holding in the fitting and sealing is achieved by some other means, such as with an O-ring. Tapered threads serve two functions -  holding in the fitting and sealing, even though sealing is usually assisted with additional sealant.

Below are the terms you need to be familiar with in order to become a thread identification expert.



Thread pitch

Thread pitch is the distance between a single thread. It is sometimes written as the number of threads within one inch distance, e.g. 8 threads per inch.


Crest and root

Fitting crest

Crest refers to the top point of the thread and root refers to the lowest point of the “valley” of the thread.


Flank angle and taper angle

Thread flank angle and taper angle


Major Diameter or OD

Major thread diameter

Posted by Joni Scott 

Topics: maintenance, technical