Threads and Threading - Sportpilot.info

1788 METRIC SCREW THREADS M PROFILE
Fundamental Deviations (Allowances): These are the deviations which are closest to the
basic size. In the accompanying figure they would be EI and es.
Fits: Fits are determined by the fundamental deviations assigned to the mating parts and
may be positive or negative. The selected fits can be clearance, transition, or interference.
To illustrate the fits schematically, a zero line is drawn to represent the basic size as shown
in Fig. 5. By convention, the external thread lies below the zero line and the internal thread
lies above it (except for interference fits). This makes the fundamental deviation negative
for the external thread and equal to its upper deviation (es). The fundamental deviation is
positive for the internal thread and equal to its lower deviation (EI).
Internal threads
D,d
D2 , d2 D1 , d1 External threads
Machinery's Handbook 27th Edition
P
2
90°
P
8
P
60° 30°
P
2
Fig. 1. Basic M Thread Profile (ISO 68 Basic Profile)
5
H
8 H
Fig. 2. Internal Thread Design M Profile with No Allowance (Fundamental Deviation)
(Maximum Material Condition). For Dimensions see Table 3
P
4
Axis of screw thread
3
8 H
H = 3
× P = 0.866025P
2
0.125H = 0.108253P 0.250H = 0.216506P 0.375H = 0.324760P 0.625H = 0.541266P
Copyright 2004, Industrial Press, Inc., New York, NY
H
8
H
4