Metric Screw Threads M Profile Machinery's Handbook, 31st Edition
2018
H 8
3 8 H
Basic Profile
d Max. Major Dia.
5 8 H
0.69717 H
H 4
0.07217 H
d 2 Max. Pitch Dia.
0.17783 H
d 1 Basic Minor Dia. (Flat Root)
R = 0.125 P
d 3 Nom. Minor Dia. (Rounded Root)
Fig. 3. External Thread Design M Profile with No Allowance (Fundamental Deviation) (Flanks at Maximum Material Condition). For Dimensions see Table 3
Basic M profile
Upper limiting profile for rounded root (See notes)
0.5 es
r min = 0.125 P
0.5 T d 2
d 2 basic pitch dia.
P 4
d 1
0.5 es
Point of intersection
d 3 max rounded root minor dia.
H 4
Point of intersection
Rounded root max truncation (See notes)
r min = 0.125 P
0.14434 H min truncation
d 1 max flat root minor dia.
d 3 min minor dia.
Fig. 4. M Profile, External Thread Root, Upper and Lower Limiting Profiles for r min = 0.125 P and for Flat Root (Shown for Tolerance Position g)
Notes: 1) “Section lined” portions identify tolerance zone and unshaded portions identify allowance (fundamental deviation). 2) The upper limiting profile for rounded root is not a design profile; rather it indicates the limiting acceptable condition for the rounded root which will pass a GO thread gage. 3) cos cos H r r T 4 1 60 1 4 Max truncation arc min min d 2 ° = − − − − m m ; E c c where H = Height of fundamental triangle r min = Minimum external thread root radius T d 2 = Tolerance on pitch diameter of external threasd
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