D’oh…I forgot what light that was and was thinking about a normal single cell tube. Yeah, looks like plenty of meat there but this will still require some care with measuring, placement, and the actual drilling and tapping. That’s really interesting about the “special” tripod threads. I’ve always assumed they were normal 1/4-20 and for the most part they are. I only have a few items here with tripod threads/sockets (mini and micro tripods, pair of binos, and two cameras) but I did a quick check with all of them. With the exception of one camera that has a nylon socket that is slightly damaged, a standard UNC 1/4-20 fits just fine. On the binos I was able to thread it in over an inch and it felt good. Nut seemed to fit fine on the tripods. One camera had a fairly loose fit on the bolt…makes me wonder if some makers bother to use the special thread and some just use the normal one. But I think for the light you can use a standard tap and be ok.
First question…do you have a drill press or access to one? I think this is kind of important here because there is limited room for error on this job (and it’s always nicer to do accurate work when you can). If not, the below still applies but you’ll have to be extra careful to stay plumb/square and steady in all operations.
So you need a way to accurately measure the thickness of the body tube, a way to accurately lay out a point down the tube that will rest more or less in the exact center of the thickest part of the tube (a normal carpenter’s combination square would be ok for this, or a cheapie sliding depth/angle gauge), a vise to securely position and hold the tube for drilling and tapping, the tap and a tap wrench to hold/drive it. Drilling an accurate depth is important here of course, and you want to go as deep as you can for the most thread engagement while still accounting for the “wasted” depth from the drill point and also leaving enough metal at the bottom to preserve integrity if the tripod screw is overtightened or something. On a drill press you can set a depth stop easily…in a hand drill you’ll have to be careful and maybe use a flag/wrap of tape on the bit since I don’t think you can find clamp-on stops for the size of bit you’ll need.
This is a relatively “large” thread and it’ll be a shallow hole, so some of the risks of not being plumb/square are lessened but it’s still very important to be plumb/square any time you are making threads. You don’t want your tripod to be cockeyed but there’s also the issue of having the hole angle matching the angle that the tap is driven into it - when they are misaligned you end up with ugly rough threads, sometimes torn metal, and this is also the #1 reason that people break taps no matter what quality they are (well, this and not using the correct drill size, both). So…highly highly recommend a drill press here, and taking care when mounting the body into the vise to get that aligned properly as best you can. If the body is tilted a tad, that’s not the worst…more important to have the drill and tap aligned together, which is easy in a drill press vs. by hand.
The “correct” standard drill bit for a 1/4-20 hole is a wire gauge #7 (that’s 0.201”). According to that .pdf on the tripod-special, they call for a 5.19mm, which is spot on with a #6 bit, a touch larger at 0.204”. Splitting the difference is a 13/64” drill bit at 0.203”. If you’re not tooled up and already have the latter, I think that’d be fine. Considering the runout and inaccuracy of hand drilling and the possibility of having that actual tripod thread (and aluminum), I’d probably opt for the usual #7 but the fractional size should be ok. Only talking a couple thousandths’ difference here but that actually does matter sometimes in metal work…and again, this application isnt’ leaving a lot of room for error and extra material/strength.
There are lots of styles of taps (lots). What you normally see in stores is called a “plug” tap…the end of it is slightly tapered and/or pointed so that it enters more easily into the drilled hole. There are also “tapered” (aka “starting”) taps which have a longer taper and narrower end….this is to help reduce errors in getting started plumb/square, but those will be much too long for this shallow hole we’re drilling. Actually the standard plug tap may also be too long and might hit bottom before getting more than a full thread or two cut. This brings us to “bottoming” taps, which is what I think I’d recommend for you here. Those still have a slight taper at the tip but are much more blunt, allowing it to go deeper into a blind/flat bottom hole for maximum thread engagement. The disadvantage of those is that it’s very easy by hand to get started crooked. If you can’t use a tap guide or put the tap holder/wrench in a drill press for accuracy, then sometimes you can use the corner of a small piece of wood board or cube and try to stay aligned right on that corner as you go (works for drilling, too).
I’ll link to some taps on Amazon US….surely something similar on the Canada offerings. Most hardware stores won’t carry bottoming taps but sometimes a good auto parts store will, if you don’t have any other tool or industrial supply houses around. Worst case I suppose you could grind down a plug tap if you have the means and an clean it up afterwards. Most hand taps are a straight flute design, which is fine. Spiral taps are all the rage these days, and if you get one of those - because this is a blind hole - you want to be sure the spiral flutes are the same direction as a drill bit where they pull the chips up out of the hole rather than pushing them forward ahead of the tap (this is ok/better sometimes for a through-hole but not what we want here). These links are for high-speed-steel taps…generally higher quality, even the cheap ones, than the normal “high carbon steel” taps and dies. The high-carbon are really more for rethreading and repairing than cutting new threads…they can work for cutting albeit with sloppier threads usually, and they are often cheaper, but I haven’t seen bottom taps in those. The cheaper China high speed steel is pretty decent for most work and not much more expensive…kind of a crap shoot in quality but workable.
For this, you don’t really need to use cutting oil but it never hurts. Use a good quality sharp drill bit, though. And use a good sharp center punch to mark the point once you locate it - don’t rely on split-point “no walking” bit designs for this, even though those are generally great. The center punch mark will ensure the bit starts where it should and this is important here. If you want to use cutting oil then a little kerosene or even crisco/lard is actually great for aluminum, so no need to purchase a bottle of fluid if you don’t want to. No need to bother with any other lube really (motor oil, household lubes, etc, etc) since they don’t do much of benefit and this is soft aluminum, brief operations, shallow hole….dry is ok.
The quality on these vary but I’ve gotten several…fairly decent. This is a set of three, one each of the different styles. Left to right: taper, plug, bottoming. Amazon.com
Same thing, bottoming only: Amazon.com
Cheaper basic spiral tap style…not sure I’d want this for this job, but it would work: Amazon.com
For wrenches, there are lots of choices at lots of price points and generally the cheapies are fine. The t-handle type are a little harder to start/keep straight unless you can chuck them in a drill press (or use a spring loaded “tap follower” in the chuck which will center itself in the divot or on the point of the heel of the tap…usually around $10 give or take) in conjunction with your vise. The straight-handle give you more leverage and can be easier to control. Just a couple quick examples that aren’t the cheapest.
https://www.amazon.com/Bosch-BTH1412-4-1-T-Handle-Wrench/dp/B07GRP817W/ (for 1/4 to 1/2 taps…that is to fit the size of the milled square flats on the tap…not actual opening size on the tool)
Amazon.com (for very small taps and up to 1/4”….not sure if either of these have the divot on the end for a follower…also not sure which would be best for whatever size the flats on a China tap might end up being…it varies…less leverage here but also less height)
Amazon.com (these from Park bicycle tool company are actually pretty nice and not expensive…a cut above most of what’s out there…this is the smaller of the two they have. made in Taiwan from actual steel instead of zinc casting)
There are some special sockets made to hold taps for use with a ratchet, and sometimes people try to use a 12-point socket on a tap the same way, but I wouldn’t recommend doing this on this job. Does make it nicer for things like automotive work where you’re repairing rather than cutting new threads, and for reaching down to difficult places or in tight corners, but sort of like the t-handle tap wrenches, using a ratchet with only one lever arm makes it super easy to get tilted and end up with terrible or cockeyed threads/broken taps when cutting new threads.
Lot of words, sorry. Figured it might be helpful since it sounds like you may be new to the tools and concept. It’s not hard to do, just a learning curve to do it right, and it can be done pretty cheaply really unless you need all the tools, vice, etc.