By my calculations, this is a nut of no known recognizable size! I don't
have a table of Whitworth nut sizes handy, and that is what it probably is.
I have one of these pump units in my spare parts box, and have taken the
following measurements:
Brass nut....0.522" across the flats
Chrome surround.....0.763" inside diameter.
The next largest SAE wrench which will fit is 17/32" (about 9 thou
larger), though a 9/16" will just grab the corners and turn it if the
nut is not too tight. However, none of my 9/16" sockets will fit into
the chrome surround, though a 1/2" will go in with a bit of room to
spare....all to suggest that a 17/32" socket, if you can find one, will
probably fit inside the chrome surround as well. When assembled, the top
of the nut is approx. 0.92" below the top of the central screw which
holds the knob, which should assist in determining what type of socket
you should get.
I think the last time I removed one of these from the dash, I used a
long thin screw driver and worked away on one flat until I got the nut
to turn.
John Slade
Manotick, ON
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