MIL-DTL-81963C
Where the shaft splining is not
20 HRC to 32 HRC
to be used as a primary pinion,
such as synchros and resolvers
Where the shaft is designed to
28 HRC to 35 HRC
be used as the primary pinion,
such as servomotors
3.4.3 Insulating materials. Insulating materials shall be used, which will enable the product to meet the
performance requirements of this specification. For additional information, see 6.12.
3.4.4 Plastics. Plastics shall be of such composition and workmanship as to enable the
servocomponent to conform to all requirements of this specification.
3.4.5 Impregnating and potting compounds. Compounds shall be used, which will enable the product
to meet the performance requirements of this specification. The compound shall not crack or flow under
the temperature range referenced in the applicable general specification. For additional information, see
6.13.
3.4.6 Dissimilar metals. Dissimilar metals shall not be used in intimate contact with each other unless
suitably protected against electrolytic corrosion. When it is necessary for any combination of dissimilar
metals to be assembled, a material compatible with each shall be interposed between them. For
classification purposes metals are grouped as follows:
Group 1
Group 2
Group 3
Group 4
Most anodic metals
Aluminum
Zinc
Copper and its alloys
Aluminum alloys
Cadmium
Nickel and its alloys
Zinc
Steel
Chromium
Cadmium
lead
Corrosion-resistant steel
Tin
Tin
Gold
Corrosion-resistant steel
Corrosion-resistant steel
Silver (Cathodic)
Most Cathodic metals
a. Contact between a member of one group and another member of the same group shall be
considered as being similar. Contact between a member of one group and a member of any other
group shall be considered as being dissimilar except for zinc, tin and cadmium as listed in Groups 2
and 3, and corrosion-resistant steel as listed in Groups 2, 3 and 4.
b. All metals not listed in the above grouping shall be considered as being dissimilar not only to
each other but also to any member of any group.
c. The above grouping shall not be construed as waiving requirements relating to the corrosion-
resistance treatment of parts and assemblies. Care shall be exercised in using aluminum alloys
against each other or against differing materials.
d. Where reference is made in the above grouping to a certain member in a particular group, the
reference applies to the metal on the surface of the part such as zinc means zinc casting, zinc
electroplate, zinc hot dip or zinc metal spray.
e. If any corrosion is anticipated between different metals in contact, even though they are similar,
the metals shall be assembled in such a manner that the smaller part is cathodic and protected,
and the larger part is anodic or corrodible.
f. Certain qualified standard or approved nonstandard parts and attaching hardware shall have tin
or nickel-plate finish. These parts may be mounted on a chassis without additional protection from
corrosion.
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