Looking for a simple solution

I look into the end of a SHCS and reliably select the wrong hex wrench.

My first thought was to train my eye to better improve my success rate. Some hex sizes are very close and I have not been able to see the difference.

My next idea was to build an axially telescopic gage that would fit in the hole. A round cross section works, I don’t need hex. Besides, I’m fresh out of drill bits that cut hex holes. This too became tricky due to very thin walls.

I also thought about an expanding gage but this too was tricky due to the 100 thou min diameter.

Does anyone have a suggestion for a simple tool?

Thanks in advance,

Rick

If you use your calipers inside jaws to measure across the vertices of the hex, then the distance across the flats of the hex (what's quoted as the hex size) is your measurement multiplied by cos(30) = √3 / 2.

So my thought would be to make up a card listing hex wrench sizes and the equivalent measurement across vertices.

My approach to this problem is a bit different. Most of the time I use the 1/4" hex bits in a magnetic screwdriver. I keep the bits ordered by size in one of these...

https://www.amazon.com/Mayouko-Magne...02&sr=8-2&th=1

magnetic holders.

I pick a bit that looks about right and test it in the SHCS. If it's the wrong size, I know I need the one next to it, bigger or smaller, and pick that up. My calibrated eyeball seldom misses the correct size by more than one so this technique works for me.

Marv,

Thanks for the quick response. We are in about the same place except my hex bits are in blocks of expanded pvc board. Yes, my eye is good enough to get within one size most of the time but Murphy always prevails and I choose the wrong one.

My hope is to find a simple one step tool or eye training that will give me the right size most of the time.

Peace,
Rick

Quote:

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Originally Posted by rgsparber

My first thought was to train my eye to better improve my success rate.

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That would be best, in my experience.

Just as I have memorized which wrench I need for different hex heads (the head and thread are standardized), the same works for SCHS. If you tend to use the same screws in your designs, you will get the correct driver.

If you are working on someone else's design, you go by thread to get the hex. Works for imperial and metric. I also look at the whole head, not just the socket. Again, that is mostly standard, folks don't want to spend extra money on fasteners, so common usage is standard hex and standard head.

In cases where frequent insertion/removal/adjustment of the screws happens, a paint pen may be an answer. A dab on the screw periphery and a dab on the matching wrench will speed things.

https://www.amazon.com/Paint-Marker-...72&sr=8-7&th=1

From my shop reference file...

HEX WRENCH SIZES

A = SAE number
B = hex wrench size for socket head cap screw
C = hex wrench size for set screw

A B C

0 0.050 0.028
1 1/16 0.028
2 5/64 0.035
3 5/64 0.050
4 3/32 0.050
5 3/32 1/16
6 7/64 1/16
8 9/64 5/64
10 5/32 3/32

Use the resistor color code to paint stripes on the wrenches corresponding to the SAE number.

You could drill holes around the lateral surface of something round and easy to carry, like a hockey puck, as a quick gauge. For example, a 1/4" SHCS has a maximum head diameter of 0.375. A letter size larger drill would be a "V" at 0.377 and allow for a little leeway yet still not fit the head of the next smaller or larger sized screws. Some trial and error may be needed. The hole could be marked on the face of the puck with the wrench size. In this case it is 3/16.

Here is a chart of US customary dimensions.

Another style could have holes drilled around the lateral edge with short pieces of each size hex wrench pressed into the holes and labeled by size. This would work better for recessed screws. Metric versions of each could be done in the same way.

Thanks for all your inputs. Here is my next step:

As a proof of concept, I 3D printed a stick 0.05” thick, 1” wide, and 6” long. It is white with black text. Total print time 30 minutes.

One edge has a series of cut outs. Between each cutout is a 0.1” wide finger. The first cut out is 5/64” wide. I increment by 1/64” up to 3/8”. All odd 64ths are labeled (5, 7, 9, etc).

I can lay a cut out on top of the SHCS and easily see the closest size. Time will tell if this tool is useful.