I like my Wera 42-piece 8100 SA 2 Zyklop Speed Ratchet Set [1/4″ drive, metric] and it sees a fair bit of professional-amateur tinkerer usage, particularly the included 8784 A1 Zyklop bit adaptor, 1/4″ (05003529001), with hex-inner or Torx drive bits. Often, though, I’ve had to dig out a separate bit assortment to get a 2.5mm inner-hex drive bit. The Wera set comes with 5 inner-hex bits: 3mm, 4mm, 5mm, 6mm, and 8mm but Wera sells bits down to 1.5mm (Wera’s 840/1 Z bits product page).
It occurred to me that I could buy the three smaller bits missing from my set, make some holes in the foam insert that fills the bottom of the set’s metal case, and add them to the kit. First, I made some measurements of the included 3mm bit and its hole:
I reached out to Wera regarding the HOP markings on these bits and heard back. According to the Wera rep who replied via email, the H signifies that it’s a hex-drive bit and the P indicates that it’s a hex-plus bit. I was surprised to learn that the letter O, however, has no significance.
The hole dimensions I got with my calipers are less accurate than the measurements of the bit because the foam is compressible and I doubt I was able to completely avoid squishing the bottom of the hole or stretching the inner walls of the hole. I’d have tried checking it with needle gauges aka gauge pins, but the hole is (as shown in the photo above) in the vicinity of 5.75mm across and I don’t have a set of 5-6mm gauge pins.
I bought them from a Taobao seller and got a 3mm bit (left in the image above) to compare to the known-genuine one (right in the photo) in the set. The screwdriver bits in the set all have a very slight yellowish cast to them. The effect is magnified in the image above. The difference, IRL to the human eye, is not so extreme. I don’t know why they have that finish, but they looked like that when I got the set and it’s not something that comes off during cleaning. The Wera page for this line of bits links a PDF datasheet but it says nada about the alloy used and/or any coatings. The finish on the newly-bought bits from Taobao matches that on the rest of the items in the set and other Wera stuff I’ve got.
There was some measuring to get the minimum distance from the edge of the foam and to figure out roughly-equidistant spots between the smallest hex sockets, using a ruler, a transparent post-it, and cut scraps of notecard. Then, I poked an awl into the spots where I was going to make the holes. Initially, I planned to drill closer to the socket holes but, after making two marks, changed my mind and went further edgewards:
I didn’t wear myself out trying to nail down the exact diameter of the existing driver bit holes in the ratchet set’s foam insert because I don’t have any fractional-size drill bits between 5mm and 6mm anyway. I did, however, need a rough-ish idea to avoid overshoooting and drilling a too-large hole and wind up not being able to have the bits held securely in place.
I used a 5mm brad point drill bit (wrapped with a piece of masking tape to indicate the depth), in a three-jaw keyed chuck attached to a knob, to hand-drill the holes. They’re overly snug and I may enlarge them if I later get a 5.5mm (or slightly larger) brad point drill or Forstner bit.