Hey there! Let's Talk Thread Dimensions!

You know, when it comes to screws, size really does matter! But how do we talk about screw sizes? Well, it's all about the thread dimensions, my friends!

(1) Pitch How far apart the threads are. (2) Effective Diameter Defined as the diameter of an imaginary cylinder at which the width of the screw groove (P/2) and the width of the screw thread (P/2) are identical. Effective Thread Area The cross-sectional area of a cylinder calculated using the effective thread diameter. This value is essential for determining male thread stress and the nut's proof load. Calculating Effective Thread Area for Metric Threads The effective thread area of standard metric screw threads can be determined using either formula (1) or formula (2) . (1)  As =π/4((d2+d3)/2)2 (2)  As = 0.7854(d-0.9382P)2 As: Effective thread area of standard metric screw thread (mm2) d: Nominal major diameter of male thread (mm) d2: Nominal pitch diameter of male thread (mm) d3: Nominal minor diameter of male thread (d1) minus 1/6 of the thread height (H)

(3) Thread Angle The angle of the thread itself. (4) Male Thread Minor Diameter The diameter of a theoretical cylinder that contacts the crests of the male thread. (5) Male Thread Major Diameter The diameter of a theoretical cylinder that contacts the crests of the male thread. (6) Female Thread Minor Diameter The diameter of a theoretical cylinder that contacts the roots of the female thread. (7) Female Thread Major Diameter The diameter of a theoretical cylinder that contacts the crests of the female thread.

Comprehensive Nomenclature for Screw Types and Thread Form Identification

Let's explore common methods for designating screw types and thread forms, including metric coarse, metric fine, and Unified coarse threads.

Screw Type Designations

Classification	Screw Types		Screw Thread Type Symbols	Screw Thread Type Examples	(Obsolete JIS)	Thread Angle
Metric Thread  Designation  (Pitch in mm)	Metric Coarse Threads		M	M6		60°
	Metric Fine Threads			M6×0.75		60°
	Miniature Threads		S	S0.8		60°
	Metric Trapezoidal Threads		Tr	Tr10×2	（TM）	60°
Unified Thread  Designation  (Pitch in TPI)	Tapered Pipe Threads	Tapered Male Thread	R	R1/2	（PT）	55°
		Tapered Female Thread	Rc	Rc3/4	（PT）	55°
		Parallel Female Thread (1)	Rp	Rp3/4	（PS）	55°
	Parallel Pipe Threads (2)	Parallel Male Thread	G （Add A or B）	G1/2A	（PF）	55°
		Parallel Female Thread	G	G1/2		55°
	Unified Coarse Threads		UNC	1/4-20UNC		60°
	Unified Fine Threads		UNF	No.10-32UNF		60°
	Whitworth Threads (3)		W	W3/8		55°
	American National Taper Pipe Threads (4)		NPT	3/4NPT		60°

(1)A tapered-to-parallel pipe thread connection is used when a tapered male thread is assembled onto a parallel female thread (Rp).
(2)Parallel pipe thread connections involve mating a parallel male thread with a parallel female thread. Both are designated with the 'G' symbol. Male threads further indicate a tolerance class (A or B), such as 'G 1/2A', while female threads simply show 'G 1/2'.
(3)Whitworth threads, originating in the United Kingdom, were phased out of JIS standards in 1968. However, they remain in use in some applications. These imperial threads feature a 55° thread angle.
(4)American National Taper Pipe Threads (NPT) share the same 60° thread angle as Unified threads.

Other screws

For reference, we present specialized thread forms, including square and sawtooth threads.

Familiarizing yourself with reference dimensions and standard terms, such as pitch and effective diameter, ensures accurate screw selection and minimizes design errors. Incorporate this knowledge into your design process.