Ashford Instrumentation Ltd - Thread Identification

Thread Identification

At Ashford Instrumentation Ltd we are often asked to identify the dimensions of the threads on the instruments we supply.

The following information has been prepared to help our customers identify the thread on the instruments they have on site.

BSP Parallel Threads

Usually initially identified as having a spigot at the bottom of the connection block (although not all will have this). This thread is sealed on the face at the bottom of the block and will usually require a sealing washer. The threads visually should be seen to be parallel when viewed side on. Male parallel threads should always be fitted into a female parallel socket.

Nominal Size (Inches) - Turns Per Inch – Major Diameter (Inches)1/8” 28 0.383 ¼” 19 0.518 3/8” 19 0.656 ½” 14 0.825 1” 11 1.309

BSP Taper Threads

Usually initially identified as having no spigot at the bottom of the connection block (although not all will have this). This tapered thread is sealed on the thread usually using PTFE tape and will not usually require a sealing washer. The threads visually should be seen to be tapered from top to bottom when viewed side on. The taper is ¾” per foot. Male taper threads should always be fitted into a female tapered socket.

Nominal Size (Inches) - Turns Per Inch – Major Diameter (Inches)1/8” 28 0.383 ¼” 19 0.518 3/8” 19 0.656 ½” 14 0.825 1” 11 1.309

NPT (Taper) Threads

Usually initially identified as having no spigot at the bottom of the connection block (although not all will have this). This tapered thread is sealed on the thread usually using PTFE tape and will not usually require a sealing washer. The threads visually should be seen to be tapered from top to bottom when viewed side on. The taper is at an angle off 1^o 47’. Male taper threads should always be fitted into a female tapered socket.

Nominal Size (Inches) - Turns Per Inch – Major Diameter (Inches)1/8” 27 0.405 ¼” 18 0.540 3/8” 16 0.675 ½” 14 0.840 1” 11.5 1.315