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Strange notch in side of case?

I recently acquired a 1959 Bulova with a 10BPAC movement (sunburst dial), which has the same identical notch in the side of the case (9:00 position in pic below) as this 10ACAC I found for sale online.

What in the world is the notch for? I know the watch I have has a lot of corrosion in the vicinity of the notch and almost looks like the case has had some water intrusion.

Thanks for any insight,

Mike

Reverend Rob's picture
Reverend Rob
Panel Member
Posted April 14, 2019 - 9:29pm

This is the notch for the static caseback, it in turn is held in place by a locking ring. This is known as the Pfisterer Patent and is the caseback locking system Bulova used on many models. The actual caseback itself has a tab that fits into the notch, and does not turn, while the locking ring does turn and secures the back.

You could think of it in terms of an anti-rotation key. If your caseback does not have this tab, it has been broken off.

Here is the original patent, dated 1951:

seabeemike's picture
seabeemike
Posted April 15, 2019 - 6:39am

Thanks!  Of course, my case back does not have the tab, which explains the interior "gunk"!