Technical assistance

Threading

Screws and nuts firmly connect machine parts so they could be easily detached when needed.That way no machine parts or screws and nuts will be damaged. Therefore this connections are called »joints that can be taken to pieces«.

Thread on screws and nuts are devided into:

Outside coils – mainly made by rolling with rolling cilinders, also by slicing with slicingjaws or turning
Inside coils – mainly made by slicing, rearly turning

Screws and nuts are outside or inside equiped with coils. To obtain a self blocking coil the pitch of the coil has to be small and the side angle big. This is attainable applying a traingle profile.

The most used coils are the metric ones with ISO profiles.

To define the coil it's necessary to be acquainted with some specific notions. Notions, marks and spelled symbols indicated on the following drawing are valid for all drawings in continuation:

d	Bolt coil big diameter
D	- Nut coil big diameter
d1	- Bolt coil small diameter
D1	- Nut coil small diameter
d2	- Bolt coil middle diameter
D2	- Nut coil middle diameter
P	- Coil pitch
H	- Coil pitch
H1	- Coil support depth
R	- Round shape radius

Coil pitch for bolts and nuts with standard or fine coil:

Standard coil pitch:
Pitch	Coil pitch
M 4	0,70
M 4,5	0,75
M 5	0,80
M 6	1
M 7	1
M 8	1,25
M 10	1,50
M 12	1,75
M 14	2
M 16	2
M 18	2,50
M 20	2,50
M 22	2,50
M 24	3
M 27	3
M 30	3,50
M 33	3,50
M 36	4
M 39	4
M 42	4,50
M 45	4,50
M 48	5
M 52	5
M 56	5,50
M 60	5,50
M 64	6
M 68	6

Fine coil pitch:
Pitch	Coil pitch
M 4	0,50
M 5	0,50
M 6	0,75
M 8	0,75
M 8	1
M 10	0,75
M 10	1
M 12	1
M 12	1,25
M 14	1,50
M 16	1
M 16	1,50
M 18	1,50
M 20	1
M 20	1,50
M 22	1,50
M 24	1,50
M 24	2
M 27	1,50
M 30	1,50
M 30	2
M 33	1,50
M 36	1,50
M 36	2
M 39	1,50
M 42	1,50
M 42	2
M 48	1,50
M 48	2

Whitworth coil

Marking sample: ¾"
(tabular measure is expressed in inches)
1" = 25,40 mm)

Whitworth tubular coil

Marking sample: ¾"
(tabular measure is expressed in
R inches – 1R" = 33,25 mm)

Inclined coil

Marking sample: S 48x3
Where the denominated diameter is 48
and pitch 3

Round shape coil

Marking sample: Rd 48x1/6"

Trapezoid coil

(normal or fine)

Marking sample: Tr 70x10

It's also important to accentuate the following:

Coil pitch determines wheather the coil is normal or fine
Fine coil has smaller depth and pitch compared to normal one
By Metric coil pitch is expressed in milimeters
By Whitworth coil pitch is expressed in number of coils on 1 inch lenght (25,40 mm)
Whitworth tubular coil is expressed in inches, in which case we have to pay attention inch is 33,25 mm and NOT 25,40 mm
There are right and left coils – mainly right is used, left only by special requests.

At BLAS-TIP we produce all bolt coils by rolling

This way we obtain the finest surface treatment and lines of force remain unbreaked making coils harder, also encreasing tractive strenght due to cold deformation of material.