Octagon recess head screw

[JDgreen227]

My aluminum utility trailer has about a half dozen of these screws, aluminum self-tapping type, that are used to hold nylon ties that secure the 12 volt wiring. While checking for a possible short in the wiring, I tried to loosen the one shown in the attachment with both T-15 (too small) and T-20 (too large) screwdrivers. It took a pair of vice grips to unthread it and once I got it out I looked closely and the head recess has EIGHT sides. Did some research and learned they are to used with a #2 Robertson (square drive) screwdriver or bit. I have seen a lot of square head recess screws on RV's but never a fastener with an 8-sided head recess.

Passing this along is my good deed for today....

 

[KennyG]

My utility trailer also has these. They seem to be very common on trailers of all sorts. I went through the same process but fortunately found out the square drive worked before i butchered anything.

 

[schmism]

8 sides means a sq head of some size should fit in and grab half the edges....

 

[Skyco]

Makes one wonder why they'd have an 8 sided hole if 4 would do and be less likely to strip...

 

[oldyellr]

Your picture is small and fuzzy, but I suspect the recess is not actually an octagon, but more of an 8-point star, or 2 square recesses, 45° out of phase.

This is a Robertson screw:

It's a Canadian patent that didn't gain a lot of popularity outside Canada because people preferred to rip off Philips designs instead of paying licensing fees. To this day the Robertson head is the most popular type in Canada because it won't strip or cam out like the Philips. You'd find those screws in all Canadian manufactured products (except automotive). Some major appliance manufacturers used the 8-point recess because it took less time to orient the driver and a tiny amount less metal. Either the utility trailer was made in Canada or a smart U.S. manufacturer used Robertson screws and drivers.

 

[Scooby074]

Its a double square I believe.

Not really a true Robertson, more of an adaptation. It can be driven with a Square Recess or Robertson bit.

 

[jeffsw6]

I have seen a bunch of those and always used a square driver on them. I thought I owned all the standard screw drivers but my guess is that screw is made so it is possible to use it with a relatively-common square driver, but can be driven with more torque by a screw gun or a robotic assembly process. Probably like Pozidrive but without the screw getting torn up the first time someone takes a Phillips to it?

 

[NHmitch]

You can find that bit at Home Depot. I use it all the time, for heavy duty screws, and my daughters swing set had this type of threading. They are called t-star screws. The "T" is for torque. I like them much better than standard philips head because they rarely, if never strip. You most likely need a T20 or T30 bit.

 

[jeffsw6]

You most likely need a T20 or T30 bit.

That's what I thought until I read his original post more closely. I don't think there is a Torx size between T15 and T20.

... I tried to loosen the one shown in the attachment with both T-15 (too small) and T-20 (too large) screwdrivers.

 

[NHmitch]

Thanks, sorry, I guess that I missed that too. Thats very interesting how they are producing the screws with the 8 star heads. I wonder if they make a special bit for this screw that you can buy commercially?