GGG-H-211D
3.9.3 class 2, lift front. The lift front assembly shall consist of two
parts: the stationary portion, which may be fabricated or integrally molded,
and a lift portion which may be fabricated from thermosetting or thermo-
plastic material, die cast aluminum, magnesium alloy, stamped drawn-metal or
other material specifically approved by the contracting activity. The lift por-
tion shall be so constructed that it will stay up or down, but will not remain
in a partially opened position (see figure 5). The lift front shall be
designed to accommodate three plates: A style c plate in the stationary por-
t ion, and a style b and style a plate in the lift part. Unless otherwise spec-
ified (see 6.2), lift front helmets shall be furnished without plates. The
lift front shall permit, without the use of tools, the removal and replacement
of each of the three plates specified herein. The contractor shall certify
that these requirements have been met.
309.3.1 Light leakage. The lift front seal against the helmet shall be free
from light leakage when tested as specified in 4.2.4.2.
Type II, handshields.
3.10
3.10.1 Handle. The handle cross section shall be securely fitted at the
lower part of the handshield. It shall be made of thermally nonconductive
material at least 32 mm in diameter with a wall not less than 1.27 mm thick.
The handle may be round, oval or triangularly shaped, and shall extend at least
130 mm below the point of attachment to the handshield. It shall be finished
smooth, knurled, or fluted. The contractor shall certify that these require-
ments have been met.
Type III plates.
3.11
3.11.1 All style plates.
3.11.1.1 Optical defects. Type III plates shall be free from striae waves,
flows, or any defects which may impair the optical quality, when tested as spec-
ified in 4.2.4.5.
3.11.1.2 Definition. Type 111 plates shall be tested for definition in
accordance with 4.2.4 .6. As a test chart, the resolving power chart pattern 20
specified in ANSI Z87.1 shall be clearly resolved with the target placed at a
distance of 10.7 meters from the telescope objective used for testing the
plates.
3.11.1.3 Prismatic power. Prismatic effects of type III plates shall not
exceed 1/16 prism diopter approximately 2.2 minutes of angular deviation),
when tested as specified in 4.2.4.7.
3.11.1.4 Refractive power and astigmatism. Type III plates shall not have
refractive power in excess of ± 1/16 diopter and the astigmatism (difference in
refractive power of any two meridians) shall not exceed 1/16 diopter when
tested as specified in 4.2.4.8.
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