Knob size

I have a gravity-fed shower (not often used) very like a bar mixer, except that it is of curved square-section, not round.

It has the flow knob on the front and the thermostatic temperature control on one end.

the flow control knob has been broken, where it fits the splines on the brass spindle.

Are these knobs a standard size? Am I likely to find a replacement somewhere to fit? It is about 10 years old and I believe it was Italian. The front is marked "termiina" and the end "OSY" but I didn't find these on a Web search.

I wondered what this was about when I saw the topic "knob size"

A new knob for a 10 yeaer old italian. (can I avoid a Michael Jackson joke?)
I doubt it very much. On both counts. What a thriller.

Shower knobs made of metal will have an inner plastic "sleeve" that fits on the splined spindle, taking up the space between the two and making installation/removal easier. If you go to your local shower showroom they might have a box of bits that you can rummage through and with a bit of luck you might find the combination of sleeve and a knob that work together.

On the italian manufacturer, have you tried going into Google Italy? You might get a better result.

Could you post a picture of the valve on here in the hope that somebody might recognise it?