seen forsterka mountains and ankarbult intended for this

摘要

The tubular roof or anchor bolt is composed of sprung steel, and pref. triangular in form. A plant expansion tool is inserted in the bolt, and expands until the bolt assumes a round shape. The anchor bolt is then inserted in the hole, and the tool is unloaded. This allows the bolt to come into pressing engagement with the inside (16) of the rock hole.