Metric Thread Verifier

Have you ever found yourself with a nut or bolt in your hand and not know what size it is?

Is it metric?

What "M" size is it?

How long is the bolt?

What size socket or spanner fits it?

What size drill bit should I use when I want to tap a hole for this bolt?

This handy little tool answers all of these questions.

There are tools out there that allow you to verify threads on nut and bolts like this one on amazon. However, these units cost money, take up quite a space in the toolbox and only answer the bolt size question asked on the previous page.

I decided that I would like to make a tool to tell me everything I needed to know.

The plan was to make a ruler style tool from some left over polycarbonate I had from an old project along with assorted nuts and bolts I had in the parts box.

I have only made one for metric threads here as I live in Ireland and we don't tend to get too much imperial stuff, that said it is easy to convert this one to imperial or even better make a tool that does both side by side.

I marked out the outline using my square and cut it out, I wasn't overly worried about perfectly straight edges as this is by no means a precision or marking out tool.

My intent was to sink nuts into the surface of the polycarbonate using heat but I didn't want to have to melt too much away or have any come back up into the threaded section.

I planned to use M3, M4, M5, M6, M8 & M10 nuts.

I drilled out holes up to the size of the spanner flats for each size, this translates to:

M3 - 5.5mm

M4 - 7mm

M5 - 8mm

M6 - 10mm

M8 - 13mm

M10 - 17mm

For the M10 I could not use a standard drill bit as my drill accommodates a max 13mm drill bit. Instead, I used a step drill. A tip here is to wrap the step drill with electrical or masking tape on the step just above your intended hole size. This way when you are drilling you can see exactly when to stop.

The reason I drilled for 2 nuts of each size is to allow one to be left as a nut in order to check bolts and the other will take a section of bolt so you can verify nuts.

I laid all of the nuts onto their final locations.

Then for the smaller nuts, I applied heat from a soldering iron, this heated the nut up until it started to melt the poly, as the nut sank in I leveled it using a screwdriver (it was super hot!) and allowed it to cool, the poly forms back around the nut and locks the nut in.

For the M8 and M10 nuts I left them sitting on the nozzle of the heat gun while set to 630 deg C, then once they were placed onto the sheet they dropped in.

The M10 got a little too hot and discoloured some of the material around it. I also burned the surface in one or 2 spots with the hot iron.

I used cut down bolts to make the studs.

To easily cut them, I put them into the chuck of my cordless drill.

I locked off the hacksaw in my vise and then ran the drill with the bolt against the blade. This is a really quick and clean way to cut bolts and I have used it in the field where I wasn't allowed to use an angle grinder.

The studs were then threaded in and some superglue put in the back to stop them vibrating loose.

I kept the M3 stud shorter than the others to try and keep such a thin bolt from bending.

Using my Dremel and engraving tool, I marked the M number of each thread. I wasn't happy with the finish so tried something else for the other markings.

After a bit of experimentation, I found that if I wrote in sharpie and then heat it for a min with the heat gun, that it doesn't wipe off.

I marked the appropriate spanner size for each nut in the test area.

Using a ruler, I copied a rough measuring guide to test the length of sample bolts.

Finally, I thought it would be handy to make a small tap drill guide to show what size drill should be used when tapping for each of the thread sizes on the tool.

I hope this one is a handy addition to your toolbox or workshop.