Torx sizes

Don't think so, never had a particular size not fit, though I don't have too many ancient ones.

Are the screws security torx screws? The have a pin in the centre and the driver has a hole in the end to accommodate the pin. The pin prevents a standard torx driver fitting.

Richard

How many sizes do you have in that set? T6 looks rather similar to T5...

Torx has half-sizes; maybe your driver is really 5.5?

The most obvious answer is the first T5 is mismarked.

You could always compare the others in the set ( assuming it is a set) with your new set to see if they are the same size, at least visually.

The torx bit is the same size on both a normal torx and a security torx

I think you have answered your own question However one of the most mind bending things I found when I worked in a store was the size of wire gauges. You had Awg, Swg, the metric measurements and the imperial measurements for the same item. You got much the same on thickness of sheets of metal as well. Then there were the bewildering sorts of screw threads, and taps and dies and of course Stainless came in different types, some were magnetic, some not and as you rightly say, the head types seemed to proliferate over time. Brian

I had the same problem with an Asus laptop recently and none of my Torx bits fitted the screws. Accidently, I found a small Torx driver lying around that had been supplied with an M2 memory case and that fitted perfectly. Looking at the end of the driver with my magnifying glass it appeared tapered.

True - they ain't something I can guess at by looking, unlike common spanner sizes.

It's a set of seven I bought ages ago. I'd guess you'd call them instrument screwdrivers. All the same length and clearly marked, T15, T10, T9, T8, T7, T6, T5. Different colour ends to the handles too.

Never used to bother what size they were - just found one that fitted the head.

I've had then so long I can't remember where I bought them.

Yes.

I've measured the diameter with a vernier calliper. Over 0.5 mm difference.

Interesting trying to find T4 (what I thought it must be) locally. Nothing at Toolstation or Screwfix, etc. Local tool shops I can remember all closed. And then remembered Belton and Slade in Wandsworth, who I was surprised to find still there. They had a bit set plus handle starting at T3 (and most of the other bit sizes like Philips, etc). Quite pricey though, but at least could collect there and then.