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Length of engagement

■Length of engagement

Thread tolerance class is chosen in consideration of "engagement classification" and "engagement length". To realize the stable tapping, it is necessary to fully understand the relation between these factors and to choose the suitable tolerance class.

On "engagement calssification : middle", the tolerance class 6H is almost always chosen for standard internal threads. However, in case of "engagement length : L", tolerance class 7H can also be chosen.

On M12x1.75, the tolerance of 7H is 25% (50μm) larger than that of 6H. And this widens the selection range of the tolerance class for taps to customer's advantage.

M12x1.75

6H Pitch diameter : 10.863 ~ 11.063mm (tolerance 0.200 mm)

7H Pitch diameter : 10.863 ~ 11.113mm (tolerance 0.250 mm)

1) Engagement classification

S L S L

M10.250.60.61.71.7M101.5551515
M10.20.50.51.41.4M101.25441212
M1.10.250.60.61.71.7M1013399
M1.10.20.50.51.41.4M100.752.42.47.17.1
M1.20.250.60.61.71.7M111.5551515
M1.20.20.50.51.41.4M1113399
M1.40.30.70.722M110.752.42.47.17.1
M1.40.20.50.51.41.4M121.75661818
M1.60.350.80.82.62.6M121.55.65.61616
M1.60.20.50.51.51.5M121.254.54.51313
M1.80.350.80.82.62.6M1213.83.81111
M1.80.20.50.51.51.5M142882424
classificationapplication
fineprecise screw threads with a little allowance
middlestandard screw threads used for machines, apparatuses and constructions bodies
coarsescrew threads used for construction and building installation, and screw threads for which threading operation is very difficult such as threading of hot rolled steel bars.
M2.50.451.31.33.83.8M162882424
M2.50.350.80.82.62.6M161.55.65.61616
M30.51.51.54.54.5M1613.83.81111
2) Classification of engagement length
M30.351133M171.55.65.61616
symbolclassifiicationlimit sizeengagement length
Sshortup to and including 2.24Pd0.2
Nnormalover 2.24Pd 0.2up to and including 6.7Pd 0.2
on rule of inter on rule of the t engagement length lassification fine L nce positionnal thr oleran S 4H loneads an ce class H N 5H gd external threads of internal threads L 6H over 6.7Pd0.2d : size designation��� ��� external thread internal thread
middle coarse5H -6H 7H7H 8HP : pitch
M3.50.61.71.755M1713.83.81111
M3.50.351133M182.510103030
M40.72266M182882424
M40.51.51.54.54.5M181.55.65.61616
M4.50.752.22.26.76.7M1813.83.81111
M4.50.51.51.54.54.5M202.510103030
M50.51.51.54.54.5M201.55.65.61616

M6 1 3 3 9 9 M22 2.5 10 10 30 30

M81.25441212M24312123636
M813399M2428.58.52525
Selection rule of the tolerance class of external threadsM80.752.42.47.17.1M241.56.36.31919
tolerance positionhg
engagement length engagement classificationSNLSNL
fine(3h4h)4h(5h4h)---
middle(5h6h)6h(7h6h)(5g6g)6g(7g6g)
coarse----8g(9g8g)