The knob you have in your hand a hundred times a day
The steam knob is one of the few parts of an espresso machine that is in constant contact with skin. It has to be easy to grip without slipping, it has to keep heat away, and it has to transfer torque cleanly to the valve spindle – every day, for years.
What goes first is almost never the function, but the surface: the knob turns dull, develops cracks or comes loose at the mount. And then there is the second case that happens in every bar sooner or later – a jug, a tamper, a careless moment, and the knob is broken.
When it is due
The knob is broken, cracked or has come loose at the mount. It spins freely on the spindle. The surface is so worn that it slips in a wet hand – with steam, that is not just unpleasant but a safety issue. Or you want to restore the look of the machine’s control area.
At a glance
| Type |
Steam knob, control part |
| Installation location |
On the outside of the steam valve assembly, on the valve spindle |
| Fits |
Rocket. The item description available to us does not say which model series the number covers – please check before ordering. |
| Scope of delivery |
One knob. Spindle, clip, cover and O-ring are separate items. |
| Part number |
M839905537 |
| Version |
Colour, material and dimensions are not documented for this number. |
| Brand |
Rocket |
Who it is for
For anyone whose steam knob is broken or can no longer be gripped safely – and for businesses that want to restore the look of a machine before reselling it or after years of use. A new knob changes the impression of the entire front.
What goes with it
The clip for the steam and water knob, the O-ring for the knob, the complete spindle for R58 and Bicocca and the Rocket accessories and spare parts category.
From our workshop in Bern and Zurich
Our routine, not a manufacturer requirement: in the evening we wipe steam knobs with a damp cloth and never with an abrasive cleaner. Milk splashes that dry on and are then rubbed off are the main reason a knob looks dull after two years. And when frothing, we hold the jug, not the knob – leaning on the knob puts a lateral force on the valve spindle that it is not designed for. Afterwards, a cappuccino as a check: Very Nutty for milk, Nutty Delight as an all-rounder, Cozy Chocolate as the sweet counter-check. More in Coffee beans.
No returns
Original spare parts are excluded from exchange and return. They are sourced specifically for each order and cannot be resold after installation or a test fitting on the machine. So before ordering, check the model, year of manufacture and serial number of your machine – or drop us a line and we will clarify the fit together. Your rights in the event of defective goods remain unaffected.
Does the knob fit my Rocket?
The part number is M839905537. The description available to us does not say which model series it covers. Send us the serial number of your machine and ideally a photo of the existing knob, and we will check before you order.
What colour is the knob?
We have no information on this, and we do not claim anything here. If the colour matters to you, we will ask before you order.
Are the clip or cover included?
No. Only the knob is supplied. Spindle, clip, cover and O-ring are separate items.
Can I replace the knob myself?
It sits on the spindle from the outside and is accessible without opening the machine. Still, disconnect the machine from the power supply first and let it cool down – the valve assembly gets hot.
Can I see the part in your showroom?
Yes. We are in Bern at Gerberngasse 44 and in Zurich at Hagenholzstrasse 50b. Bring the serial number of your machine or simply the old knob, and we will compare directly.
Questions about the fit? Write to us at [email protected]. We deliver across Switzerland and to Liechtenstein in 2-4 working days.
