Picture of Spanner Wrench for a Watch Case
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

Picture of 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

Picture of 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

Picture of 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

Picture of 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

Picture of 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.

Picture of 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.
john.mck11 month ago

Here's a short video I made:

Phil B (author)  john.mck11 month ago
Very good. Thank you for sharing.
graydog1112 months ago

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.

3366carlos8 months ago

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

tassie24 years ago
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!
Thank you for this brilliant tip.
Con Peters, Netherlands.
tassie2 tassie24 years ago
hi pic enclosed re vernier watch tool. tassie 2 australia have a nice day
Phil B (author)  tassie24 years ago
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.
billtr96sn3 years ago
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.
Phil B (author)  billtr96sn3 years ago
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.
stienut4 years ago
Great ible. Just made one, took about 45 minutes. I used a dremel with a cut-off wheel, can't imagine hand filing it.
Phil B (author)  stienut4 years ago
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.
Solderguy5 years ago
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.
Phil B (author)  Solderguy5 years ago
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. 
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 B (author)  Solderguy5 years ago
 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.
This is a great idea. I signed up for an account just to get back onthis posting and give props to whoever came up with the idea. My wifeand I have matching Fossil watches and I couldn't figure out a way toget that back off of it when the battery died. Great Thinking!!
Phil B (author)  BenhamCollectibles5 years ago
Thanks for your comment.  I hope you enjoy Instructables. Many things posted here would be of little use to me, but I guessthe ones posting feel passionate about them.  If the thickness ofthe mending plate exceeds the width of the indents, you can also do alittle grinding or filing near where the mending plate spanner wrenchengages the indents.  It should make a good tool for you that willnot mar the cases of your watches.  You probably know you can clickon someone's hot linked screen name to see their profile, where you canalso find a listing of other things they have published, in case theyhave done other things of interest to you, as well.  
klee27x5 years ago
You can cut a nice spanner wrench out of a hack saw blade. They're high carbon steel, and the result is very nice - flat and shiny. If I still had mine, I'd post a pic.

Phil B (author)  klee27x5 years ago
 Thank you for your comment.  A couple of years ago I took my watch to a jeweler.  The watch had stopped briefly.  He opened and closed the case with his spanner wrench.  When I recently needed to change the battery I found the case back was so tight that I needed to put my homemade spanner in a vise and twist the watch with two hands to get the back to loosen.  From past experience with hacksaw blades, I think the corners of a spanner wrench made from one would have broken off.  Perhaps hacksaw blade steel would work fine most of the time.
rimar20005 years ago
Phil, I looked "astuto" in Google translator, and found the following: crafty nombre: 1. colic adjetivo: 1. cannie 2. smart 3. clever 4. sharp 5. politic 6. knowing 7. wide 8. worldly-wise 9. pawky 10. shifty 11. sleeky 12. slick 13. devious 14. guileful 15. canny 16. tricky 17. leery 18. sly 19. foxy 20. wily 21. artful 22. crafty 23. cunning 24. dodgy 25. astute 26. deep I think CLEVER is the word fro you!
Phil B (author)  rimar20005 years ago
Thank you, Osvaldo. I am glad you did not choose shifty, devious, guileful, foxy, or dodgy. Those all imply dishonesty and character flaws. You are a good friend.
Some wars were caused by inexperienced translators ...!
Phil B (author)  rimar20005 years ago
Also some very funny stories about things that did not cross language barriers well. Clarol makes hair care products. One is a curling iron that sprays a water mist. Its name is "Mist Stick." Clarol decided to sell it in Germany, but did not change or research the name. In German "Mist" means cow manure. "Stick" (spelled Stueck) sounds the same, but means "a piece of..."
I'm a machinist by trade, but I guess that makes me a bit heavy handed for watch repair (I always end up scratching something, always). Making tools is one of my favorite things to do as well, so I may end up doing this if my usual way fails (take a large rubber stopper and press it to the back and turn). Making tools is so gratifying, I bet it felt good when it first turned.
Phil B (author)  VagsmaCutter5 years ago
Thanks for your comment. Making a tool is gratifying. You might enjoy some of my other Instructables. I enlarged a saw blade hole to fit the arbor on a Sawsmith, ground an adjustable wrench down to make a cone wrench for a bicycle hub, converted a fisherman's scale to a bicycle torque wrench, made a carbon arc torch for a stick welder, worked the wear out of the indexing holes on a Craftsman radial arm saw, cut a shovel down to about 3/4 size for a lady, built a saw table for ripping and crosscutting with a wood lathe, and made a fixture for using an angle head grinder as a cut-off saw. There is enough information in what I have written for you to search and find them. I hope you enjoy them.
Koosie5 years ago
Nice, a simple, quick solution for time-consuming problem :)
jcard215 years ago
I let my watch guy replace my SEIKO quartz watch batteries, because he will inspect/replace the rubber gasket, plus add silicon to lubricate it, so when the back is re-installed, it will not "bind" and tear the gasket. He doesn't charge me for little things. Example: My 1960 LONGINES Automatic (NOT quartz/no battery!) stopped a week or two after being serviced by him. I brought it back. He immediately opened the back, and there must have been a speck of dirt lodged inside, because he just touched something inside, and the watch immediately started running again, and has been running ever since. (He did say it could happen again.)
TabLeft5 years ago
Cool, I always just use needle nose pliers though.
Phil B (author)  TabLeft5 years ago
That is also a possibility. I have found the points of the pliers tend to slip out of the indents unless ground flat on the sides. I did that with a couple of pliers in different sizes for working on some camera lenses.