| 摘要 |
1493357 Manhole covers BRITISH STEEL CORP 14 March 1975 [19 March 1974 12 June 1974] 12114/74 and 26067/74 Heading E1G A triangular or other manhole cover 2 has on its underside three bearing portions 6, 7, 10 spaced around its periphery (e.g. at its corners) for seating on respective bosses 16, 17, 19 of a frame 1, the two portions 6, 7 comprising shallow lugs, Fig. 4 (not shown), presenting engagement surfaces 8, 9 parallel to the plane of the cover while the third portion 10 comprises a downwardly tapering boss 11 presenting to the frame boss 19 a wedging surface 12 sloping downwardly away from the line joining the other two bearing portions. The triangular half-cover shown has on its outer edges two corner lugs 20 which are pressed against a frame wall 21 by the action of the wedging surface 12. |
