Erbauer Ground HSS Drill Bits 7 x 109mm 5 Pack (29283)

Hello, Thank you for your enquiry. The fluted part of the bit is around 75mm. Hope that helps. Thank you for using Q&A.

Hello, This really depends on the steel (i.e mild/stainless etc) and the thickness of the steel. It also depends on what power tool you're using. You can have the best drill bit in the world and still not make a dent if your drill isn't powerful enough. For mild steel this drill bit should be fine (however, for concrete ideally you should use a concrete bit (diamond tip for extra durability). The Dewalt Cobalt drill bits are also very good for drilling metals and are more hard wearing then the erbauer bits so would be better suite if you're drilling multiple holes. Thanks for using Q&A.

Hi SeanTX, Yes, High Speed Steel (HSS) drill bits are recommended for drilling RSJs. Thanks for using Screwfix Q&A. JT

Hello Decklover, This product will drill a 3mm hole so in order to get the screwthreads to bite into the wood you'll want to use a 4mm screw. Thank you for using Q&A (CW)