Replacement PTFE Case Back Gasket for Citizen AT8020 Blue Angels

Product Overview

This is the case back gasket for the Citizen Eco-Drive Blue Angels — the thin white sealing ring that sits between the case back and the case, and the part that quietly decides whether the watch stays watertight. It is cut for the Blue Angels case and made from PTFE, the material most people know as Teflon, in the flat white I-ring profile used for case back and crystal seals.

Every time the case back comes off — a capacitor or battery service, a movement repair, a full restoration — the old seal should come out with it. Once a rubber gasket has been compressed for years it stops springing back, and refitting a flattened ring is how moisture gets in. This replacement drops into the same groove, sits flat under the case back, and restores the seal without changing anything about how the watch goes together.

The people who order it are usually the ones who look after their own watches: an owner doing a routine service, a hobbyist restoring a Blue Angels picked up second-hand, or a watchmaker who wants the correct seal on the bench before the case goes back on. If you already shop for custom fluororubber material watch straps to change how the watch looks, this is the other half of the same job — the part that protects what is inside rather than what is on the outside.

Water resistance is not a property of the case alone; it is a system, and the case back gasket is the joint in that system that gets opened most often. The ring weighs 7 g and is easy to overlook, which is exactly why it is the most common reason a freshly serviced watch starts fogging up.

Why PTFE Outlasts Rubber

• PTFE, not rubber — The ring is polytetrafluoroethylene, sold for decades under the Teflon name. It is a flat I-ring rather than a moulded rubber O-ring, and it holds its shape under compression instead of taking a permanent set the way rubber does.
• Heat resistance — Temperature swings between a cold wrist, a warm room and a hot car do not soften the ring or change how it seals. Rubber gaskets harden with age and heat; this material keeps its sealing integrity through the same conditions.
• Chemical resistance — Sweat, soap, sunscreen, salt water and everyday moisture do not attack it. That matters here, because the case back is exactly where sweat and rinse water pool.
• Long-term stability — It does not harden, crack or lose elasticity the way an ordinary rubber seal does, so it still behaves the way it did on the day it was fitted.
• Even compression — The flat I-ring profile spreads seating pressure evenly around the groove. A static seal wants steady, even squeeze all the way round, not a rubber bead that flattens on one side.
• Flexible to fit, firm once seated — The ring bends easily in the hand, so it drops into the channel without twisting or fighting back, and it lies flat once it is home.
• A different job from a strap — Unlike a fluororubber material watch strap, which flexes every time you move your wrist, this seal is compressed once and then left alone. That is the application PTFE is built for.
• Made to the seating dimensions of the case — It is cut to the groove it is designed for rather than trimmed from generic stock, so it sits level instead of riding up on one side.

Specifications

Model & Case Number Matching

1. Turn the watch face down and read the case number stamped on the outside of the case back. On the Blue Angels it is a short alphanumeric string printed below the model name — that string, not the dial design, is what decides whether a gasket fits.
2. Cross-check it against the reference on your paperwork or warranty card. Both Blue Angels references use the same case, so either one is a match for this ring.
3. If the case number is worn or unreadable, check the movement marking visible through the case back and choose the matching order option. The three options on this listing correspond to the three versions of the watch.
4. Measure nothing else. This is a case back seal, not a strap — lug width, strap length and buckle size have no bearing on whether it fits. Buyers who shop for a fluororubber material watch strap online often assume the same measurements apply here; they do not.
5. Note the number down before you order. It is the single detail that decides fit, and if you are picking up a custom fluororubber material watch strap at the same time it is worth having both matched to the same watch in one go.

Replacement Timing

• Every time the case back is opened — a battery or Eco-Drive capacitor service, a movement repair, a crystal or dial job. A gasket that has been compressed for years has taken a permanent set and will not seat as tightly the second time, however good it looks.
• If the watch has fogged — a faint mist under the crystal after a swim, a shower or a hot day is the classic sign that moisture has already crossed the case back. By the time you can see it, the seal has been leaking for a while, and trapped moisture corrodes the movement and hands.
• If the old ring has visibly changed — look for a gasket gone hard and shiny, flattened into an oval cross-section, cracked at the fold, or stretched so it no longer sits in its channel. Any one of those means it has stopped sealing.
• On a second-hand or vintage Blue Angels — you have no way of knowing whether the last service included the seal. Changing it is a quick way to rule the question out before you wear the watch anywhere near water.
• Before the watch goes back into regular water use — the 200 m (20 ATM) rating on this model assumes every seal in the case is sound. The case back gasket is the one opened most often, so it is the one that most often lets the rating down.
• What the watch faces day to day — hand washing several times a day, rain, summer sweat, chlorinated pool water, sea water on holiday and the temperature change of a hot shower. Each is minor on its own; across a service cycle they add up, and the case back is where they concentrate.
• Before you fit a new strap — if you are changing how the watch looks, it is the natural moment to deal with the seal. A spent gasket is like a worn-out fluororubber material watch strap: still in place, but no longer doing the job it was fitted for.

Installation & Pressure Testing

1. Work on a clean, well-lit surface with a soft mat under the watch. A case back tool can slip, and a scratch on a polished case does not come out.
2. Open the case back with the correct case back wrench, or a Jaxa-style tool fitted with the right dies. Do not lever it with a knife or a screwdriver.
3. Look at how the old gasket sits before you lift it — which way up, how deep in the groove. A photo on your phone saves guesswork when the case goes back together.
4. Lift the old ring out with a plastic-tipped tool. Never scrape the channel with metal: a burr in the seating groove will leak whichever gasket you fit afterwards.
5. Clean the groove completely. Wipe out dried residue, old grease and any grit with a soft swab, then let the channel dry before the new ring goes in.
6. Seat the new I-ring flat, pressing it in evenly with a fingertip or a plastic tool so it sits level all the way round, with no twist, no fold and no high spot.
7. Check that it has not stretched. The ring should rest in the channel under its own weight; if it rides up on one side, lift it out and reseat it rather than forcing the case back down on top of it.
8. Refit the case back and tighten evenly, working across the case so it seats square. Over-tightening distorts the ring rather than improving the seal.
9. Pressure test the watch afterwards. Most watchmakers and jewellers can do this on a wet or dry tester, and it confirms the seal is holding before the watch goes back on your wrist.
10. Note the date for the next service. A seal changed on schedule is a seal you never have to think about.

Ordering & Delivery

Choose the order option that matches the version of your watch. The three options on this listing are not interchangeable, so it is worth reading the marking on the case back before you add the part to your basket. If nothing on the watch matches what is listed, send a photo of the case back and the dial first and we will point you to the right one.

Fuerman supplies replacement watch parts and custom fluororubber material watch straps, so a watch can be re-sealed and re-strapped in a single order. Covering both at once means opening the watch only once, and it also means the band and the seal are matched to the same watch rather than bought at random. FKM fluororubber, silicone quick-release and leather bands are all available in the widths most commonly needed.

Packing, shipping and lead time are confirmed at the time of order, because all three depend on where the parcel is going. If you need several pieces for a workshop or a resale order, tell your sales contact the quantity you have in mind so availability and terms can be checked before you commit.

The ring is beige-white, and like any small part it can look slightly cooler or warmer depending on your screen. It sits out of sight once the case back is closed, so the tone matters far less than the fit. Check that the ring seats flat before you grease or fit anything; if it does not sit level, get in touch rather than forcing the case back down on top of it.

Fogging & Seal Checks

• One joint, not the whole case — this ring renews the seal at the case back only. Fogging means moisture has crossed one of the case's seals, and the crown gasket, crystal gasket and case tube are the other joints a watchmaker should look at in the same inspection.
• Read the symptom before you order — a faint haze that fades once the watch warms on the wrist usually supports a small amount of moisture. Visible droplets, or water sitting against the inside of the crystal, mean a larger breach and a watch that should come off water duty straight away.
• Trapped moisture keeps working — every day it stays inside it goes after the movement, the hands and the dial, and on an Eco-Drive it can reach the light-charging components as well. Leaving it until the next service is how a gasket job becomes a movement job.
• Do not try to dry it out at home — a hair dryer, a warm oven, a bag of rice or a spell on a radiator pushes moisture deeper into the case and adds heat and dust damage on top of the water.
• Leave the controls alone — pumping the crown in and out, or working the pushers, drags water past those seals too. Keep the watch closed and get it to a bench.
• When fogging returns after a new gasket — the case back joint was not the only leak. Ask for the crown gasket and crystal gasket to be checked as well, and for the seating groove in the case back to be examined for burrs or scratches that would stop any ring from sealing.
• Confirm with a pressure test — a watchmaker's wet or dry tester is the only reliable way to know the watch holds its 200 m (20 ATM) rating again. Fitting the ring and hoping is not a test.
• What this gasket cannot do — it will not repair a damaged case, worn case back threads, a failed crystal seal or a corroded movement. Those need a watchmaker, and the case back ring belongs inside that repair rather than instead of it.

Gasket Appearance & Storage

Once the case back is screwed down, this ring disappears. It sits inside the joint between the case back and the case, so from the outside — on the wrist, in a photo, on a shelf — there is nothing to see. It shows only with the back off, and even then it reads as a thin flat white line resting in its groove rather than as a coloured part. That is worth knowing if appearance is part of your decision: the beige-white tone belongs to PTFE itself rather than being a finish applied for looks, and it has no effect on how the ring seals. If the part that arrives looks slightly warmer or cooler than it did on your screen, that is the display rather than the gasket — colour differences of that kind are normal with small pale components, and it is worth noting that product colour may vary slightly from the images for this reason.

A spare is worth keeping flat, in the bag it arrives in, somewhere dry at room temperature. A house drawer or a parts box on the bench is ideal; a hot car, a sunny windowsill, a damp workshop sink area and a bathroom cabinet are not. Keep it away from oils, greases, solvents, fuel and penetrating sprays, and out of any tray where loose screws, tweezers or tools can nick the edge. PTFE takes the shape it is stored in, so never fold it, stretch it or test-fit it by hand to check the size — a ring that has been bent will not lie flat in the groove and cannot be pressed back into shape. If a stored ring picks up dust, a wipe with a dry swab is enough; it needs no grease and no other preparation before it goes in. Write the case number on the bag so the next service does not begin with a measuring check, and if you are already ordering a custom fluororubber material watch strap, adding one spare gasket to the same parcel saves a second wait when the watch comes apart again.

Technical Support & Model Matching

FUERMAN has been supplying watch parts and accessories from Huadu District, Guangzhou since 2010 — 15+ years in the trade, a 60-strong team and a deep ready stock held in China. Our technical team, which includes technicians with 30+ years of watchmaking experience, matches items to your watch by brand, model or reference number before you order, so you know it will fit. Send a photo or a measurement if you are unsure: we will confirm the right choice, talk you through fitting, and stay with you afterwards — troubleshooting, replacement parts and after-sales help long after your order arrives.

FAQ