Threads have a gender—either male or female. The threads are on the outside of a male fitting and on the inside of a female fitting. The outer diameter is smaller on a male thread than a female thread because the male end compresses into the female end.
Measure the thread diameter with your caliper. For male threads, measure the Outside Diameter (O.D). For female threads, measure the Inside Diameter (I.D).
Male thread fitting - a male thread has the grooves known as the thread on the outside (externally). Female thread fitting – a female thread has the grooves known as the thread on the inside (internally). You will find examples of this on nuts and bolts.
A straight thread has a constant nominal diameter across its length, whereas a tapered thread does not. Measure the nominal diameter of a straight thread at any point. For a tapered thread, measure the nominal diameter at the 4th or 5th thread from the head to get the true measurement.
Measure the Inside of a Female Thread Port:
If it is 19.1mm Internal Diameter — then the actual port size is a Female 1/2" BSP Thread. If it is 24.6mm Internal Diameter — then the actual port size is a Female 3/4" BSP Thread. If it is 31.0mm Internal Diameter — then the actual port size is a Female 1" BSP Thread.
The first number follows the Gunze Count standard and indicates the thread size. The larger the number, the finer the thread (a 50/2 will be thinner than a 30/2). The second number indicates the number of strands, or plies, twisted together.
There are different types of threads found, and some main types of threads are parallel threads, including BSPP, UN/UNF, and metric parallel. The second type of thread is tapered threads in which metric tapered, BSPT, and NPT thread/NPTF thread are included.
Male threads are on the outside, like a bolt. Female threads are on the inside, like a nut.
The terms male and female always refer to the threads on the fitting. The male threads are on the outside like a bolt. The female threads (female fittings) are on the inside like a nut. Male threads screw into female threads.
FPT Female Pipe Thread (interchangeable with NPT) FPT is a term for pipe fittings that MIP (male iron pipe) or MNPT (male national pipe thread) fittings fit into. Female threads are internal located inside of the pipe or fitting.
The main difference between rolling threads vs. cutting threads is that cut thread bolts and screws have the same body diameter as thread diameter. Cut threading takes a steel bar and cuts the threads into the material. If you start with a 1-inch bar, your bolt or screw's threads and body will still be 1 inch.
Red Thread: true love. 2. Orange thread: true friendship. Yellow thread: family love. Blue thread: people who love each other, care for each other, but aren't soulmates.
Thread Size / Weight
For example, if a thread is labeled 30 wt., it means there are 30 kilometers of thread that weighs 1 kilogram. A finer thread, such as 50 wt., would have 50 kilometers in that same 1 kilogram bundle. Bottom line: the thicker the thread, the smaller the number.
The 'A' designates an external thread, and 'B' designates an internal thread. • Classes 1A and 1B are considered an extremely loose tolerance thread fit. This class is suited for quick and easy assembly and disassembly. Outside of low-carbon threaded rod or machine screws, this thread fit is rarely specified.
Threads are only symbolically represented on drawings; therefore, thread notes are needed to provide the required information. A thread note must be included on all threaded parts, with a leader line to the external thread or to an internal thread in the circular view.
Inch thread sizes are specified by diameter and threads per inch. Diameter is also known as screw size. For those with a diameter smaller than 1/4", screw size is indicated by a number (e.g., #10 or No. 10). For example, a 10-24 screw has 0.190" thread diameter and has 24 threads per inch.
As the name suggests, TPI is measured by counting the number of thread peaks along a 1 inch length. The TPI measurement is then often affixed to the diameter of the thread to form a common imperial thread size, e.g. '1/4-20', which would denote a ¼ inch diameter, and 20 threads per inch.
The thread pitch is the distance between each thread in mm. For example, an M10x1. 5 (coarse) thread has a 1.5mm pitch, while an M10x1. 25 (fine) thread has a 1.25mm pitch. To simplify metric thread callouts, the international (ISO) standard for metric threads eliminates the pitch callout on coarse threads.
National Pipe Taper (NPT) are a standardized fitting that is commonly used for joining pipe. Due to the tapered threads (wider diameter at the base of the threads, similar to a trapezoid) the male fitting will tighten the further it is threaded into the female.
NPT and BSP threads are generally not compatible due to the differences in their thread forms. NPT threads have a 60° included angle and have flattened peaks and valleys (this is a Sellers thread form); BSP threads have a 55° included angle and have rounded peaks and valleys (this is a Whitworth thread form).
To determine the NPT size, with a caliper, measure the diameter of the 2nd or 3rd thread on your pipe, fitting or valve as shown below. Find the caliper measurement in the chart and cross reference the nominal NPT pipe size. Don't get confused, the actual measurement is not the same as the NPT pipe size.
Many pipe threads must make not only a mechanical joint but also a leakproof hydraulic seal. This is accomplished by the tapered thread form of the male matching the thread form of the female tapered thread and the use of pipe sealant to fill any voids between the two threads which could cause a spiral leak.