Heller ® 6 Piece HSS-Co Cobalt Drill Bit Set - 2mm - 8mm Quality German

On the whole good. 1 bit did blunt rather quickly.

Worked on hardened screws that needed removing

I drilled stainless 1mm plate fourteen times with one small drill using cutting paste. I kept coating drill bit every six seconds to keep bit cool and lubricated. Stainless- for example being very hard- must be drilled at a slow speed. I used a battery drill on the approx 200 rpm setting. or four revs per second. If you use full speed you will destroy the drill bit and get nowhere.Been there many times. Well worth the money if you follow these guidelines. If drilling a big hole start small and work up through the drill sizes. Drill bits usually snap when finishing the hole as they create a rag. You can feel the end of a hole coming and you should ease off to a light pressure to avoid breakages. Good luck.

These did the job for me, drilling through a rounded titanium screw and through a titanium exhaust. I used some soldering flux to keep it wet/cool and it was done in 10mins and bit end is almost same as before, it did wear down a bit though. Would buy again if needed and excellent value for money.

These drills are durable and have kept their edge with the moderate jobs I require them for.

With all the various jobs I become involved with, I find myself purchasing a variety of drill bits for differing applications, and with varying results. These Heller bits were bought primarily for the purpose of drilling through stainless steel, something that requires patience and a control of drill speed, not forgetting coolant. Having achieved their objective in this instance, I have been using the bits for numerous jobs, and every time, the work in hand is easily carried out, as the bits treat any material like butter.Overall, great value ... and with the correct care and attention during use, these bits will certainly far exceed the lifespan of other, less effective drill bits.

I bought these to drill out a small bolt shaft that the head had sheered off of on the underside of my bonnet. The two smallest bits did a fantastic job and were able to drill through the length of the bolt but the middle bit snapped immediately I got it going in the hole. I would have expected the smaller bits to have broken instead.So now I have a broken piece of cobalt drill bit stuck in the middle of the broken bolt. That's not going to be easy to fix.

Very brittle two snapped after 30 seconds