United States Patent 2668763
Publication Date:
02/09/1954
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Primary Class:
Other Classes:
106/271, 252/187.200, 106/243, 430/432, 106/2
International Classes:
G03C5/40; G03C11/04; G03C11/00
Foreign References:
| GB191113088A | ||||
| GB261201A |