Bob,  Here are some definitive specifications on the Wurlitzer 165
tracker bar, taken from the Seabreeze Park Wurlitzer 165 duplex roll
frame tracker bar, which is an original.

The hole spacing is, as Robbie says, .1227" on centers.  The holes are
broached square except for the bass drum and snare drum holes which are
round and slightly elevated.  The square holes will just accommodate
a no. 52 drill when it is rotated.  (A no. 51 drill will fit, if the
flutes are turned so as to lodge in the diagonally opposite corners of
the square; but the drill will not rotate.)  The round holes will take
a no. 45 drill.

The square holes are, in my opinion, not worth the extra work of
broaching, unless authenticity is your aim.  T.R.T. tracker bars
were made with round holes, and I don't think anybody could tell, by
listening to a band organ play, whether the tracker bar had round or
square holes.  What matters more to the quality of the music is the
quality of the cutting that produced the roll, and mattering even more
is the condition of the organ and its valve work.  The late Steve
Lanick used to broach the holes in the tracker bars he made, and he
would usually break a few broaches in the process.

The tracker bar measures 10-7/16 inches from end to end, not including
the attachment ears.  With the ears included, the length of the bar is
11-1/8 inches.  The face plate of the tracker bar overlaps the side by
about 5/16" and is soldered to it.  The depth from the crown of the
face to the back of the bar, not including the gasket, is 1-1/8 inch.
The overall height of the tracker bar is 1".

Wurlitzer would have used a white gasketing leather.  Someone like Art
Reblitz could tell you what kind of skin it was; but I don't recall.
Johnny Verbeeck re-gasketed our tracker bars and used a brownish
leather.

With a dust screen made of brass screen, as is usually found in
Wurlitzer 165's, the Verbeeck gasket tended to leak.  But we switched
to using a fine fabric mesh that was once used in computer glare
screens.  That is extremely satisfactory: the weave is finer and it
catches more particles, and the screen stays in place on the two posts
that center the tracker bar on its backing board, when you remove the
bar to clean the screen.  A swipe by a camel hair brush does the job.

Brass dust screening tends to curl, lift off, and fall down into the
organ works.  I can no longer find any glare screen fabric, but I'm
sure nylon or poly screening used in laboratory work and sold by places
like Small Parts will work perfectly, if you get the right mesh size.

The one thing I can't explain is the purpose of the two vertical slots
on the face of the tracker bar, one on each end of the bar.  The slots
are a little less than 1/16" wide, and are positioned so that the edges
of the roll paper ride in the middle, more or less, of each slot. They
may be intended to assist in the paper alignment, but you can't really
use them for that purpose, because the paper alignment is best done by
assuring that the perforations center on the tracker bar holes.  Those
mysterious slots allow you to look into the tracker bar interior, and
you can see the two holes in the back of the bar where the bar
alignment posts enter.

If you've ever seen the inside of a Wurlitzer tracker bar, you will
notice that it is mostly hollow, with 75 nipples soldered to the face
and back of the bar to form the airway channels.  I wrote a year ago
or so an article for, I think, the "Carousel Organ" giving my theory
on how such a complexly engineered bar was made.

Matthew Caulfield