For secure and reliable fixing of items and fixtures to masonry, concrete, brick, block etc.. Requires 13mm spanner to tighten hex. nut. Internal eye diameter: 20mm. For facing bricks/ concrete/ 7N concrete block drill 14mm hole for the expansive bolt.. (Low density aircrete block or mortar may require a 13mm hole) NOTE: These expansion bolts are not suitable for works requiring Building Control or Local Authority sign-off such as safety rails, balustrades, load-bearing joists/ wall plates etc