Spanner Wrench for a Watch Case




About: I miss the days when magazines like Popular Mechanics had all sorts of DIY projects for making and repairing just about everything. I am enjoying posting things I have learned and done since I got my first ...

My watch has a screw- in back on the watch case. It is possible to order a universal spanner wrench for around $10 US. I wanted to make my own spanner wrench so I can replace the battery without needing to get to a store that can change it for me.

In the photo you can see the indents for the spanner wrench so it can unscrew the case back.

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Step 1: Use a Mending Plate

I used a 1/2 x 2 inch mending plate. These are available in any hardware store. Any thin piece of steel would work, too. (The photo is from Google Images.)

Step 2: Mark the Area to Grind

I like to make markings for cutting or grinding steel on masking tape. The markings are easier to see. Cover the mending plate with masking tape. Mark the edges of the spanner wrench indents.

Step 3: Rough Grinding

Grind away most of the steel that will need to be removed, but do not go too close to the marks for the indent edges.

Step 4: File to Fit

Use a good file to remove the amount of steel required for a very precise fit on the back of the watch. Check your work frequently.

Step 5: The Wrench on the Watch Case

If all was done properly, your new spanner wrench fits the indents very neatly. Remove the tape. Grasp the spanner wrench between your thumb and first finger. If the case back is on very tightly, you may need to grasp the mending plate spanner wrench with a slip-joint plier. Hold the watch firmly with your other hand and twist in a counter-clockwise direction.

Step 6: The Back Is Off.

Here you see the back of the watch case removed. Replace the battery. Be sure to get all gaskets, etc. back in place. You may want to turn the back of the case counter-clockwise until you feel the threads fall in so you do not jamb the threads by cross threading.

Step 7: Easy to Carry

The last time I changed my watch battery I slipped my spanner wrench in to my wallet and changed the battery immediately after purchasing it at a store that does not change batteries for customers.

You can also see that I cut a second profile on the other edge for a watch with a different size back. Now my one wrench allows me to change the battery in a second watch I came to own.

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34 Discussions

Phil Bsjdaskldd

Reply 2 years ago

The one problem with changing your own battery is that the "O" ring seal may need to be replaced. If it does not seal properly, perspiration may get into the watch and create other problems. Having the battery replaced by a shop means you will have a functioning "O" ring. So, there is that to be considered, too.


4 years ago on Introduction

Wow, although I already have the correct tool I am going to make one of these anyways. A fantastic idea


Reply 4 years ago on Introduction

This worked!!! I used a thick board and heavy gauge finish nails. I flattened out the end of the nails with a hammer, and put the watch in a vise to keep it from moving. Just saved me a couple bucks! Thanks!


4 years ago on Introduction

Good 'ible Phil.

A word of caution though:

Do not touch new battery contact points with your fingers. Handle battery with a cloth or paper towel. Your fingers are coated with natural body oil, which can cause a bad connection when installed. Really, this applies to all batteries in flashlights, toys, etc.


5 years ago on Introduction

great idea, too bad I already bought the watch tool from harbor freight.


9 years ago on Introduction

Maybe this is here on site, but.. A Vietnamese watch repairer outside the train station near my house did thousands of batteries on watches. For commuters in a hurry. His tool of choice? A metal vernier caliper measuring tool. A lot of people here will have one in their workshops! Multi adjustable of course.. Unless a watch was xxx tight he could unscrew and replace a battery in about 45 seconds! Always puffing air into back of case first to clear any dust. The good quaility eg Mitutoyo verniers with a screw lock are ideal You can lock them in place. Load on them is negligable in the scheme of things. He always sat his watches on a sandbag/ soft support. For xxx heavy watchbacks he had a real watch undoer as a backup. Seldom he used it! Like I say he did thousands.. Pic uploader not working for me... will try a pic send for you guys later!

3 replies
Phil Btassie2

Reply 9 years ago on Introduction

That is a better quality caliper than those I see at a local home improvement store. There is an actual adjustable tool for removing the back from a watch case. I would think the price difference between it and a better caliper, like the one shown, would be small. My Instructable was designed to service one or two watches an individual might own. The man you mentioned must be able to service many different watches, all with a different size case.


7 years ago on Introduction

You can also use a pair of scissors. I take no responsibility for you cutting you fingers off though.

One thing I would like to add though, do not overtighten the back of your watch when you replace it.

1 reply
Phil Bbilltr96sn

Reply 7 years ago on Introduction

I have also used a pair of needle nose pliers. For a while I had a couple of cameras I worked on when they needed it. I filed flat sides on the tips and they made good spanner wrenches for such things. Scissors and needle nose pliers do slip more easily than the tool I showed here.


9 years ago on Introduction

Great ible. Just made one, took about 45 minutes. I used a dremel with a cut-off wheel, can't imagine hand filing it.

1 reply
Phil Bstienut

Reply 9 years ago on Introduction

There was a time when I did not have a Dremel. Thank you for taking a look at this. I am glad it is useful to you.


10 years ago on Introduction

I think I love you. I have a mechanical watch that got waterlogged, andI wasn't able to open it. I'll try your instructable and post the results.

3 replies
Phil BSolderguy

Reply 10 years ago on Introduction

I have heard of soaking a waterlogged instrument, like a watch or aspeedometer, in alcohol.  The alcohol absorbs the water.  Ihope all goes well for you. 

SolderguyPhil B

Reply 10 years ago on Introduction

The home-made spanner wrench I made worked flawlessly. I first made onefrom a broken hack saw blade, but it was too flimsy, so I got a steelstrip and used a dremel to cut a groove in. I had to put the spannerwrench in a vice and twist the watch with both my hands because it wasso stuck in there. I'm happy because the inside isn't rusted to nothing(all the gears are brass), so all I have to do is free a few gears fromthe grip of the rust and it should work. Thank you so much. 5/5

Phil BSolderguy

Reply 10 years ago on Introduction

 Great!  I had not thought of a Dremel, probably because I didnot own a Dremel when I made my spanner wrench.  If yours is a goodwatch, it might be worth a cleaning by a watchmaker (if it does notbegin to work as is).  Thanks for the report.