Sep 18, 2026Buying Guides
Watch Case Opener Buying Guide: Jaxa Wrench, Friction Ball or Case Knife
Which watch case opener do you need? How to tell snap-on, notched and branded case backs apart, what to measure, and the Jaxa sizes, friction balls, knives and BRL/PAN dies we list.
Three case back types, and how to tell them apart
Almost every case opener question starts the same way: which type of back does this watch have? There are three, and you can tell them apart by looking at the rim of the case back.
Case back type | How to recognise it | Tool that opens it |
|---|---|---|
Snap-on / pry-off | smooth rim, often a small lip where a blade can enter | case knife, then a press to close it again |
Notched / screw back | notches, slots or two small holes around the rim | adjustable case wrench, or a dedicated die |
Multi-corner / branded profile | a polygonal or branded outline with no standard notches | a die cut for that specific profile |
If the back does not clearly match one row, that is the most common reason to write to us — a photograph of the back settles it faster than a description.
Measure before you ask
The size that matters is the case back itself, measured across its widest point — not the case, not the bezel, and not the strap width. Calipers are best; if you only have a ruler, lay it flat across the back and measure twice.
For notched backs, the useful figure is the span between two opposite notches. For two-hole backs, the distance between the centres of the two holes — not the outside edges.
Write the measurement down to the nearest 0.5 mm. That single number decides most of the answers below.
What we list, by tool family
The table below copies the figures from our own listings. Where a listing does not state a figure, the cell says so rather than guessing.
Tool | What the listing states | Listing |
|---|---|---|
Jaxa-style wrench, medium and large backs | ABS, 7 inch width, 17.2 cm long | |
Jaxa-style wrench, XL / wide backs | steel | |
Jaxa-style wrench, battery-change kit | steel, 5.9 cm width, 16.5 cm long | |
Friction ball | rubber, 7.1 inch | |
Case knife set, 4 pieces | stainless steel; two blades 91 mm x 9 mm, two 91 mm x 4 mm | |
Case knife + battery remover kit | stainless steel | |
Adjustable suction opener, 8 non-marking pads | aluminium alloy | |
No.5537 opener set, 6 sizes | metal, listed for 18.5–29.5 mm, model SP000059 |
Dedicated dies for branded case backs
Some backs have no notches at all — just a shape. Those need a die cut for that shape. We list dies by their code:
We also list a die and hand-tool set recorded for the Omega 5700 series, 508 and 510 calibres: Omega 5700 series die set.
The die codes above are stated on our listings as the fit for the profiles they name. We are an independent supplier of aftermarket and genuine parts. We are not affiliated with, authorised by, or a dealer for any watch brand, and a die code appearing here is not a statement of brand endorsement — it is the code the listing carries so you can match it to the back in front of you.
Jaxa wrench, friction ball, or knife?
Each of the three fails in a different way, and the failure is worth knowing before you buy.
If your case back is | Use | Why the others struggle |
|---|---|---|
notched, small to medium | a Jaxa-style wrench with the matching die | a friction ball cannot grip notches; a knife can mark the rim |
notched, wide | a Jaxa-style wrench, XL | a standard wrench may not span the back |
smooth, flat, no notches | a friction ball | a wrench has nothing to seat into |
snap-on with a pry lip | a case knife | a wrench and a ball both need a feature to hold |
A knife that slips tends to mark the case. A ball that cannot grip tends to slip without warning. A wrench with the wrong die tends to chew the notches. That is why the measurement comes first.
Before you order
Every item above is confirmed by message rather than sold from a price list. Send the measurement you took and, if you have one, a photograph of the case back, and we will confirm which opener or die matches and reply within one working day.
That is also the right message to send when your back is not in any table on this page. Sizes outside our listed range, older case profiles and unusual branded shapes are exactly what we check by hand.
FAQ
I measured my case, not the case back. Is that the same?
No, and it is the most common mix-up. The case is the whole body; the case back is the removable disc. Measure across the disc.
My wrench came with dies but none seems to fit.
Send a photo of the back next to the die that is closest. Notch shape matters as much as the span, and a die that is slightly too large will slip before one that is slightly too small.
Can I open a screw-back with a friction ball?
Only if the back is smooth. If it has notches, the ball has nothing to grip and will spin.
Do these tools work on any brand?
They work on a case back shape, not a brand. Match the shape and the measurement, and write to us if you are unsure — we would rather check than have you buy the wrong die.
