Patent ID: 6860690

Claim:
A first screw member for threaded connection with a second screw member by relative motion about a center axis, said first screw member comprising: a screw body; a screw thread formed by helically protruding from said screw body, said screw thread having two linear thread flanks and formed with a notch groove at a top portion of said screw thread, said notch groove having a flat bottom; a first crest portion formed around said top portion of said screw thread, having a first inner surface extending into said notch groove of said screw thread and having a first linear flank continuous to one of said linear thread flanks; a second crest portion formed around said top portion of said screw thread, having a second inner surface extending into said notch groove facing said first inner surface via said notch groove, and having a second linear flank continuous to the other of said linear thread flanks; said first linear flank and said second linear flank of said first and second crest portions being provided to form an intersection angle to be set smaller than a flank angle formed by said two linear thread flanks; and said respective crest portions being provided to bite into said second screw member when said first screw member is thread-connected with said second screw member.