When I need a T27 I grab one of the hundreds of weed eater tools we have at work. You could never lose all the ones we have. Chainsaw tools, though, are a rare thing indeed. I think we're down to two at the moment.
Hollow ground flat tips are hard to find in anything that isn't an X-in-1 style driver, which is a shame. The tapered ground flat tips make great pry bars but lousy screwdrivers on anything old and crusty. More often than not a 4-in-1 does the job but a dedicated driver that was readily available would be nice.
There is actually a reason for taper ground flat head screwdrivers.
Originally, the slot in screws was hand cut into the screw.
This appears to have been done using a tapered knife file on old screws I’ve seen.
A tapered knife file has a similar taper to the taper on a tapered flathead screwdriver.
Because of the taper on both, a screw with a taper cut slot can be pushed onto the head of a tapered flathead screwdriver and stay put, similar to the advantages to the genuine tapered “Robertson” Square driver screwdrivers.
If a screw slot gets buggered, you can also recut the screw slot with a knife file and continue using the screw without issue, other than a slightly larger slot. It’s a tapered driver, so it doesn’t really matter if the slot gets cut deeper.
I’m not sure exactly when screws started being mass produced with parallel machine cut slots (probably after the US Civil War), but there was still a reason tapered screwdrivers continued being used, other than the popularity for them as a pry bar.
Older tapered head flathead screwdrivers used to come with the tapered heads ground to a very fine taper.
With wider screw slots this tended to seem annoying.
It’s actually an intentional advantage.
The screwdriver tip can be ground down slightly, easily, with a grinder or file, making the tip slightly thicker, so you can get an exact fit to the width of the screw slot, or just slightly wider, do there is a wedging action when the screwdriver is inserted.
The sides of the tapered flathead can also be slightly filed for width.
The general goal for mechanics was that you filed screwdrivers custom for odd sizes, and made up a bunch of drivers for all the screw sizes you routinely came across.
The system actually works pretty well.
To make the screwdrivers grip even better, a checkering file (used for making checkered patterns on gun grips) can be used on the screwdriver tip, making horizontal grooves that help prevent the tip from slipping, sort of like the serrations on ACR Phillips head bits.
Some manufacturers sell drivers with these serrations already cut. Facom does this, or did on their older tapered drivers, and unlike some of the US made drivers that did similar, Facom used finer serrations.
A Facom driver when properly fitted to a slotted screw will stay in place horizontally, sticking out from the screw slot when the screw slot is also turned horizontal, on a vertical wall.
I’ve done it with screws on lights witch plates on the wall, with a 12” long Facom driver.
The only screws that really needed hollow ground screwdrivers previously were on guns and fine machined equipment, were the screws were usually custom, and the item really expensive.
Gunsmiths were usually taught how to custom make “turnscrews” (the old fashioned name for a screwdriver) to custom fit the very fine slots found on some firearms.
Here are a couple videos from Brownells showing turnscrews being made.
Brownells sells a huge variety of different widths and thicknesses of screwdrivers bits with parallel flat heads for different slot sizes.
https://www.brownells.com/gunsmith-...-bits/magna-tip-super-set-bits-prod41568.aspx
And sets.
With Brownells MAGNA-TIP screwdriver, it is now possible for the gunsmith and firearms hobbyist to have a close fit in most any gun screw he will encounter - and darn near everything around the house and garage too. DESIGN OF BITS The TRUE hollow-...
www.brownells.com
. That reminds me in need to get a T27 bit socket to have at the house. Have the driver and the provided tool.
