drill bits

[greengrass]

I have four bits for a drill. One I've discovered is classed as a 'Saw bit' but cannot find a tool comapany that shows the other bits, each of which has a cutting area about 12-15mm holes they cut 8 6 & 4 mm but what makes them different from ordinary bits is the fact I have to set the drill in reverse for them to drill out a hole. Normal direction they don't drill just put a mark in the wood. Anyone any idea the purpose of the small bits?
Many thanks
Bob

 

[ColJack]

those would probably be screw extractors..

they bite into the stripped heads of posi or philips screws and reverse them out..

 

[greengrass]

I have four bits for a drill. One I've discovered is classed as a 'Saw bit' but cannot find a tool comapany that shows the other bits, each of which has a cutting area about 12-15mm holes they cut 8 6 & 4 mm but what makes them different from ordinary bits is the fact I have to set the drill in reverse for them to drill out a hole. Normal direction they don't drill just put a mark in the wood. Anyone any idea the purpose of the small bits?
Many thanks
Bob

Hi coljack Many thanks now I understand, I shall try a couple of screws i've tried getting out and no joy.