What is the purpose of the strip of wood on top of the keys going diagonally across the the bottom right of this picture?



It's one of Eddie Twang's shots of an Ibach grand in this thread.

To keep the keys from falling off when moving the piano.

That's what I thought, but are they common?

Very common. I can't think of a brand that does not have them.

About a month ago I was called to tune and fix a Kimball La Petite grand. It had no rail. It had recently been moved and you guessed it; the keys were all out of place and jammed.

It also protects the key from being inadvertently pushed upwards.

... and the keys being levelled after someone has broken the slots cut into its screws!

On a Steinway it will stabilize the treble end of the keyframe. It will flex without it present and affect setting of the shift position stop. Very heavy spring involved.
All the best!

Sure it may help, but keeping the pedal movt extremely tight is also a good precaution. indeed the action cannot really be "retained" by the pedal movement, but I try to have a bit of the pressure on it (the paper sheet can be pulled out)
This, may compress and move a bit with seasons certainly but if it can help the key frame I am for it (key frame tend to warp where they are cut for the UC movment I've find)