Types of Threads

The screw thread is often shortened to the thread, is a helical structure used to convert between rotational and linear movement or force. A screw thread is a ridge wrapped around a cylinder or cone in the form of a helix, with the former being called a straight thread and the latter called a tapered thread. A screw thread is the essential feature of the screw as a simple machine and also as a fastener. According to its position in the body is divided into external thread(male), internal thread(female), according to its cross-sectional shape (dental) is divided into triangular thread, rectangular thread, trapezoidal thread, zigzag thread and other special shape thread.

Thread Handedness
The helix of a thread can twist in two possibledirections. Most thread s are oriented so that the threaded item when seen from a point of view on the axis through the center of the helix, moves away from the viewer when it is turned in a clockwise direction, and moves towards the viewer when it is turned counter clockwise. By common convention, right-handedness is the default handedness for screw threads. Therefore, most threaded parts and fasteners have right- handed threads.

Thread Gender
Every matched pair of threads, external and internal, can be described as male and female. For example, a screw has male thread, while the matching hole has female thread.

Thread Design
The type of thread can be identified by the following characteristics.

The pitch is the distance from the crest of one thread to the next inmm.TPI (Threads per inch) is used by inch thread. 

Thread Diameter
The major diameter is determined by the thread tips.The minor diameter is determined by the groove of the thread.The pitch diameter is the distance of two opposite flanks or the distance of the centreline of the profile.

Thread Angle
The flank angle is the angle between the flank of a screw thread and the perpendicular to the axis of the screw. Tapered threads have a taper angle. This is the angle between the taper and the centre axis of the pipe.

Types of Threads
●Metric Thread(M-ISO)
●UNC/UNF Thread
●NPT Thread
●BSPP Thread
●BSPT Thread

COMPARISON SHEET (M – BSPP – BSPT – NPT – UNC - UNF)

Metric	BSPP(G)	BSPT(R)	NPT	UNC/UNF
Type	Parallel	Parallel	Tapered	Tapered	Parallel
Flank angle	60°	55°	55°	60°	60°
Thread angle	0°	0°	1°47′	1°47′	0°
Seal ocation	O-ring/ Gasket/	O-ring/ Gasket/	On threads	On threads	O-ring/ Gasket/
	Cone	Cone			Cone
Thread per Inch
	BSPP(G)	BSPT(R)	NPT	UNC	UNF
1/16”	28	28	27
1/8”	28	28	27
1/4”	19	19	18	20	28
3/8”	19	19	18	16	24
1/2”	14	14	14	13	20
3/4”	14	14	14	10	16
1”	11	11	11.5	8	12

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