United States Patent 3451621
Inventors:
Splinter, Donald H. DE.
Publication Date:
06/24/1969
Other Classes:
238/287, 238/349, 238/310, 238/283
International Classes:
E01B9/02; E01B9/48; E01B29/24; E01B9/68; E01B9/00; E01B29/00; E01B21/04; E01B9/00; E01B13/00