QISF 7Pcs 300mm Extra Long Twist Drill Bits Set (4-12mm）+ 9Pcs Woodworking Drill Bit Depth Stop Collars Ring Locator (3-16mm)，for Wood Hole Cutter Drilling DIY Plastic

So I read the reviews and “go slowly and carefully “ was definitely my summary. I needed these quite urgently and there isn’t much other choice out there so I went for it, I needed to drill a 25 cm hole in some fairly hard wood.Started off ok but as the 4mm bit got hotter it actually started to unwind! Never seen that before. Allowing it to cool gave a bit more use but after a while it was like jelly and I had to reverse very carefully so it didn’t snap and leave 20cm of drill bit in my wood which would have been a nightmare. I then switched to the 5mm bit and it coped better as it now had a pilot hole but it also started to do the same thing but finally got to the end. So I just about made it but both bits are now in the bin. I understand something that long at 4mm is going to take a hell of a lot of stress so it can’t be expected to be infallible.. so I’d like me you need one job urgently, please go carefully but I managed to get to the end without a disaster (did take 30 mins to drill a single hole though!) . But they will definitely not last under frequent use IMO

Used both the 4mm and 5mm bit for drilling pilot holes. After drilling approx. a dozen pilot holes with each drill in softwood, both resembled a melted Curly Wurly chocolate bar. I had to postpone my DIY task, unfortunately. Was not an expensive product but I thought they would have been able to fulfil my expectations.

The 4mm lasted only a few seconds before it unravelled and broke. The 5mm lasted slightly longer before it twisted and ripped the wood out of the vice and flung it across the workshop. Not willing to try any of the other sizes and returning all as sub-standard.

Bought these to use for some drilling required on my deck. For limited use they are brilliant. Not sure how good they would be for trade use but for the occasional DIY cannot fault them. the depth spacers are very handy and good value.

Use the thinner drill bits carefully not to snap them. They are thin and will definitely break as I found out. Having said that they do work just fine, but I wouldn’t recommend using such a long thin drill bit in hard wood.

While most drilling jobs only require standard length drill bits, sometimes extra deep holes through thick materials need long series drill bits. These perform well in wood and plastic, and the depth control sleeves give accurate hole depth.

I was drilling pilot holes in railway sleepers to make flower and vegetable boxes for the garden.They needed to be long bits to get through the 200mm depth.I managed 6 holes and when I’d drilled those, the ‘twist’ had straightened out.I tried a slightly larger bit to see if this was Any better, but again, after 6 holes, the twist had gone. This made the bits too unstable to use and I gave up and bought some expensive ones from a specialist store, which I have to say, were no problem to use.

After reading some of the reviews here I decided to give them a go hoping they would last for the small amount of use I needed them for. First hole drilled fine but the 2nd hole proved too much. The metal is very soft and the slightest bit of heat makes them bend like rubber and literally unwind. Would not recommend.