2232218-A is referenced by 3 patents.

A bolt or screw (2) has an external screw thread (4) for screwing into an object, a first internal thread (6) of the same hand as the external thread (4) and engageable by an externally screw-threaded tool (not shown) for driving the bolt or screw (2), and a second internal thread (8) of opposite hand to the first and external threads (6, 4) and engageable by a different screw-thread of the same (or a separate) tool for unscrewing the bolt or screw (2). The end (10) of the screw or bolt (2) and the engaging end of the tool are convex or concave to avoid binding, or they may be flat. Where both the external tool threads are on the same tool, the central portion is of hexagonal cross-section. A release washer may be positioned between the head (10) and the tool or tools.

Security fasteners for preventing theft or vandalism
Application Number
GB19890012714 19890602
Publication Number
2232218 (A)
Application Date
June 2, 1989
Publication Date
December 5, 1990
Yarrow Frederick John
Yarrow Frederick John
F16B 23/00
F16B 23/00
B25B 13/00
F16B 23/00
B25B 13/48
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