Document Type and Number:
Japanese Patent JPH0372993
Kind Code:
U
Application Number:
JP13521789U
Publication Date:
July 23, 1991
Filing Date:
November 21, 1989
Export Citation:
International Classes:
E21B1/00; B28D1/14; E21B21/00; (IPC1-7): E21C7/08; B28D1/14; E21C3/00