Mechanical interlock
Structural Fixings for Ductwork Systems BG 10/2010, By Glenn Hawkins, Published by BSRIA in 2010, states in relation to the working principles of structural fixings: ‘Keying (or mechanical interlock) is the working principle of screws and undercut anchors. As a self-tapping concrete screw is driven into a pre-drilled hole, it keys into the structural base material. An undercut anchor keys into the base material as it is tightened to a specified torque. Hole depth, hole diameter and anchor embedment depth are key criteria that affect performance of these fixings. Keying is also one of the key working principles of direct fastening systems, which drive hardened nails into the structural base material using specialist power tools. Direct fastening also uses bonding and clamping principles too.’
--BSRIA
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