Allen Key Size

Here is a chart.

...and Here is a chart in metric.

Note that the head will change the hex driver size for any given screw size.

Hello Doorman

Don't know if I'm missing something, but I couldn't see anything about wrench dimensions (across flats) on that link.

It's on http://www.valvias.com/miscellanea-allen-din-912-bolt-thread.php for metric bolts. Also found one for inch bolts which gave wrench A/F as 0.75 x bolt nominal dia.

BTW how do you rename a link (like you did)? I saved mine in Favourites with a new name but when I copied that into CR4 it wasn't live.

Cheers........Codey

Codey, the second chart from the top is the metric application chart. The left hand column is the across flats dim of the hex wrench. For example, it shows the 3mm as the correct size for a M4 cap screw (matching your linked chart), a M5 truss head screw, and a headless M6 set screw.

To make a link text read as part of a text, type out the text as you wish. Highlite the desired text; when you do and there is a copied site address on your clipboard, the 'Globe and Chain' icon on the toolbar enables. Click on the icon (or CTRL-k), and paste in the address.

Hello Doorman, I was missing something, I was reading the left-hand column as the bolt nominal size.

I think I've got the hang of the link, thanks. I put a website on this mytext as a test. It doesn't open if I click on it here, but if I paste it into Word it works, so hopefully when I've submitted this post it will be live.

Cheers.......Codey

Yep, the link is active for me.

Another tool in your CR4 toolbox!

Formula D = 1.5d gives approx answer only. M10 bolt has 17mm head (across flats). M12 has 19mm. That's for standard metric bolts, though you sometimes come across specials.

There's plenty of data on the web for full range of diameters.

For eg : for 10 mm Hex bolt , the spanner size is 15 mm ( formula is D = 1.5d ).

Few 10 mm bolts have 15 mm heads. There is no formula for hex head bolts, nor for allen head screws.

A trip down memory lane reminds me that for set screws (recessed), the allen key will be 1/2 the diameter of the screw.

Don't know if it applies to metric,but it does work for sae.

Key dimensions vary depending on the type of head , button ,countersunk , standard cap and specials as mentioned before.

The key size should be able to apply the recomended maximum torque.

There is no mathematical formula for knowing the key size. In bolts also thumb rule of D=1.5d applies only for standard bolts. For heavy duty hex bolts this formula do not hold good. Similarly for Allen keys also depending on the service, hex socket of the allen bolts varies in size depending on the torque required for tightening to achive the bolting effect. As thumb rule up to 3mm allen bolt minus 0.5 mm is key size, above this up to 6mm bolts size minus 1mm is key size above this upto 16mm minus 2 mm is key size but after that it changes.