| 摘要 |
A self-tapping masonry screw comprises a shank 2 formed with a rolled helical groove 5 next to one or two helical ridges 6 & 7, and with a land 9 relative to which the ridge(s) is raised and the groove 5 is depressed, the axial width of the land being at least 4mm and at least 50% of the land diameter, and the helix angle of the ridge is at least 10 degrees. <IMAGE> |
