The small ring that keeps the rotary knob cap in place
On top of the steam and water rotary knob sits a cap – with a logo on some series, without on others. It covers the screw underneath and gives the knob its smooth top. It is not held by a thread but by an O-ring that clamps it in its seat.
This is not a part that is under pressure. Even so, it is one that regularly gets lost: when the ring loosens, the cap pops out the next time you grip the knob firmly and eventually ends up under the machine or in the drip tray.
When it is due
The cap is loose, can be lifted with a fingernail or falls out when you turn the knob. That is the whole diagnosis.
A second sign is a cap that holds but sits crooked. In that case the ring is squashed on one side or torn.
If you have already lost the cap, you need both: the cap and this ring. A new cap on an old ring rarely holds for long.
At a glance
| Type |
O-ring, clamping ring |
| Installation location |
Steam and water rotary knob, under the cap |
| Fits |
Rocket machines for which the manufacturer lists part number A449904672 |
| Scope of delivery |
one O-ring, without cap |
| Part number |
A449904672 |
| Material |
Elastomer |
| Brand |
Rocket |
Who it is for
For anyone whose rotary knob cap no longer stays in place, and for workshops that have taken a knob apart.
This is one of the few parts in this area that you can replace without tools and without a technician – the cap sits on the outside and is separate from the water path.
The O-rings and sealing rings in the Rocket catalogue
Rocket fits a whole series of O-rings in the steam path, water path and boiler that look very similar from the outside. For most of them, the documentation gives neither the inner diameter nor the cross-section – they can only be reliably told apart by the part number. That is why we list them individually, with the number in the title or in the table:
-
O-ring steam and water tap – A449904334
-
O-ring for the steam and water tap cap – A449904672
-
O-ring steam and water rotary knob, Cellini and Giotto – C400002786
-
O-ring water nozzle, Appartamento to Mozzafiato – C400003008
-
O-ring 3-way valve – M449907403
-
O-ring S2 valve – M449907143
-
O-ring 4250 silicone, R9 – M449905837
-
O-ring 3187 Viton, R9 – R499907384
-
O-ring drain elbow, Boxer, RE A and R9 – M449905463
-
Copper sealing ring heat exchanger – C479900673
-
O-ring boiler top, Porta Via – A449906261
-
O-ring boiler bottom, Porta Via – A449906262
-
O-ring heating element, Porta Via – A449910266
-
O-ring 18 × 5 mm machine foot, R Cinquantotto – A449906954
If you measure the part you removed and do not know the number, send us the model and serial number – we will check it against the exploded view.
What goes with it
We stock the matching caps individually: Cellini and Giotto, with R logo and without logo.
Also matching are the rotary knob Cellini and Giotto, the rotary knob Appartamento TCA and Bicocca and the clip.
You will find more control parts in Rocket accessories and spare parts.
A small trick from our workshop: when fitting the cap, we do not press it in with a thumb – we lay a soft cloth over it and press with the flat of the hand. That way the ring gets even pressure and the chrome-plated surface of the cap stays free of marks. It is our habit in Bern and Zurich, not a rule. Afterwards, an espresso made with Nutty Delight is well deserved – after all, the cap is back in place.
No returns
Original spare parts are excluded from exchange and return. They are sourced specifically for each order and cannot be resold once they have been installed or test-fitted on a machine. So before ordering, please check the model, year of manufacture and serial number of your machine – or drop us a short message and we will clarify the fit together. Your rights in the case of defective goods remain unaffected.
Frequently asked questions
Is the cap included?
No. Only the O-ring is supplied. The caps are separate items and differ depending on the series.
Is this ring under pressure?
No. It clamps the cap in its seat. It has nothing to do with the steam path.
Can I replace it myself?
Yes. This is one of the few items in this area that can be done without tools and without opening the machine.
What are its dimensions?
No dimensions are documented for this item. The binding reference is the number A449904672.
Can I see the part at your showroom?
Yes. We are in Bern at Gerberngasse 44 and in Zurich at Hagenholzstrasse 50b. Bring the part you removed and we will compare it with the replacement on site, so you only take home what really fits.
Questions about the fit or the serial number of your machine? Write to us at [email protected]. We deliver across Switzerland and to Liechtenstein in 2-4 working days.
