DeWalt 7mm Extreme 2 HSS Drill Bit
does the job, very hard!
What can I say? it's a drillbit. Unusual tip shape helps stop it wandering on hard surfaces, lasts very well, seems well made, will be buying more as I need them, especially as 7mm seems to be the size most sets exclude for some strange reason.
3 Dec 2014
Works on cast iron.
I had to shorten some lengths of cast iron guttering and needed holes for the fixings. Normal bits would barely touch the cast iron. One of these bits did the job although it did take about an hour for each hole! Not sure I'd want to do it often but will definitely be using these bits if I do.
Trick I found is to do it slowly and let the bit cool down regularly as it seems to cut better when cold.
23 Jul 2013
perfect for what i need , can be used several times on material i need to drill, before needing another one , and i do put these dill bits through there paces with the job i do
31 Aug 2011
These bits are in a different league to standard twist bits.
Precise tip does indeed allow you position the hole precisely. It soon bites, and in wood, will plunge itself straight in.
In fact it can be a bit too agressive, and you generally need to brace yourself to prevent it screwing itself into the workpiece. This also means some care is needed to give clean entry and exit in wood.
Bits are just as impressive drilling into steel. Very sharp and effective.
23 Mar 2011