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GMP Tools manufactures pentagonal head bolts to secure manhole covers. That’s right, not square, not hex, but pentagonal — another case of security through obscurity. Of course, if you sell bolts with heads that have an odd number of sides you need to supply the corresponding tools to turn them, so they also sell two different sockets: one with a 7/16″ hex drive for impact tools, another with a 19mm hole which you can turn with a rod.

The bolts come in two different sizes. The first measures 3-1/4″ long and has a 5/8″ – 11 thread with a chamfer under the head for countersinking. The second measures 1-7/16″ long and has a 1/2″ – 13 thread with a flat shoulder under the head. GMP tools machines both types of bolt from a “tough grade” of stainless steel.

The 3-1/4″ bolt runs about $25, while the shorter 1-7/16″ bolt runs $15. Remember: to drive these bolts you’ll either need the hex drive impact socket, which runs $40, or the socket with the hole for $14.

Manhole Cover Bolts/Wrenches [GMP]
ManHole Cover Bolt Wrench [Craftwork Tools]
Manhole Cover Bolt Impact Socket [Craftwork Tools]

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15 Responses to Pentagonal Bolts For Securing Manhole Covers

  1. FredB says:

    I have on my desk here (wave in front of monitor) a bronze pentahead bolt. These things are used on covers over gas and water shutoff valves. This one has a dash of yellow paint on it so, I assume it was on the cover over a gas valve. The socket for this bolt is available for about $6.

  2. Mr P says:

    http://keyedlok.com/ are the best with the high security screws while the bolt is a little more standard looking with out the fender washer built into the bolt its allot cheaper with there most expensive 3 1/2 in 1/2 13 thread going for $8.50 and cheapest for 3/8 $4.15

    They do have the coolest looking security screws I have ever seen.

    Ye I know were going to have the argument that it can be defeated with a hack saw, dremmel, easyout, mold making ect.. But they are great deterrent and when deeply countersunk nearly impossible to defeat with out the proper pit

  3. JT says:

    Fire hydrants have had a pentgon turning head for years!

  4. @JT:

    I had to walk down and look at the fire hydrant on the block. Yes, it does have Pentagonal headed caps and valve stem. I never noticed.

    Now I have to find some manhole covers — all the manholes(and covers) are either buried or ripped out because they are rebuilding the streets.

  5. fred says:

    Around here, fire hydrants have a stainless steel cap with a raised cross on its top. The cap is free spinning – and you need a wrench that has a strong magnet in the drive end. The magnet pulls the drive shaft up into the cap at the same time as the wrench engages the cross on the cap – allowing you to operate the hydrant.

    There are other hydrant security systems:


    The problem with any sort of raised pentagon – is that you can grab hold of it with a pipe wrench.

  6. Dan Lyke says:

    My first reaction to the end of this article, ” Remember: to drive these bolts you’ll either need the hex drive impact socket, which runs $40, or the socket with the hole for $14″, was to add “or a big beefy pair of Vise-Grips”, but Fred beat me to it with the pipe wrench suggestion.

  7. @Dan Lyke:

    When’s the last time you saw a manhole cover in the middle of the street with a bolt sticking out above the surface?

    Like Mr P says, they are counter sunk or counter bored so the head is below the surface of the manhole cover. How are you going to get a pipe wrench or vice grips on them?

    I guess my point in the post was that is that you can go to the internet and order just about any security pattern and have it that week. Or if you’re handy take a few measurements and go make something in your shop. Security bolts like this are just a deterrent for somebody passing by, not a planned attack.

  8. Joe C. says:

    Slightly off-topic, but the use of security bolts on restroom stalls has always puzzled me a little. Is (was) there a big problem with people disassembling the panels to warrant using these fasteners?

    I guess the lack of reading material in commercial bathrooms gives me too much time to think about stuff like this.

  9. David Bryan says:

    I was looking at the GMP Tools website and found these manhole cover bolts and wrench (the one for the rod) on page 23 of their 1960 catalog. They’ve got partial 1949, 1952, and 1960 catalogs on the site, and they’re worth looking at. I get a kick out of looking at things like their pipe ripper and that pipe spreader with a handle “made out of 1 1/2″ steel pipe for lightness”.

  10. Fritz Gorbach says:

    I’ve always been curious about those restroom stalls too. Who could disassemble and then steal a 4 x 6 panel from a public space, unnoticed?
    Anyway, snapon sells some of these pentagon sockets, also, and I always wanted to get some, you know, just in case.

  11. Zathrus says:

    Who said anything about stealing?

    I suspect that they’re done this way just to prevent vandalism.

    Of course, I’m sure everyone here was an upstanding teenager and Eagle Scout, and never would have done anything of the sort in their youth.

  12. Alan says:

    Yup. My son’s former high school has a senior prank tradition. Couple of years ago they decided to remove all the partitions from the bathrooms.

    Unfortunately for them, the school administration starting talking about severe retribution so they got scared and dumped all of partitions into the woods. Of course, they were destroyed in no time turning a harmless prank into a major vandalism.

    Glad I talked my son out of participating. Some better security fasteners would have stopped this.

  13. Nate says:

    This is also used on high-voltage electrical enclosures, among other places. Searching for the trade name, “penta wrench” or “penta socket”, will find more sources. There seem to be at least two sizes in common use.

  14. kyle says:

    http://www.globalfasteners.com/tamperproof.htp has many diferent kinds of tamperproof bolts and screws including the penta bolt and the penta nut

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