wrote in message
Hmmm; maybe you don't know what I mean. The registration pins printers
(used to) use are little metal tabs

The pins (about the size of a pencil eraser) can take several forms:

o pins inserted into, say, a negative carrier
o pins inserted into a registration board
o pins inserted into a support board for use in a vacuum frame
o pins inserted into a printing press
o pins inserted into a bar
o pins that can slide in a bar
o pins spot welded to a little thin metal disk - used loose
o pins spot welded to a small shim-stock metal rectangle,
the rectangle is taped to the table/carrier/whatever

It is the punch that is the big item in all this. If the
system uses round pins then the distance between the punched
holes has to be held constant.

Since nothing can be held constant, the punch usually makes
one round hole and one or more slotted holes so the location
of the second hole(s) isn't so critical. It is possible to
punch a round/slotted hole systems by hand with a pair of
1-hole punches, though not recommended.

Very large films use a central round pin and two slotted pins
along the long side and a round 'tail pin' in a perpendicular
slot in the middle of the opposite edge. The punches for this
work are large and expensive.

Punch systems are ANSI/ISO etc. standard.

In graphic arts the punch registration system is used all the
way from the initial films, through the contacting films and
printing plates and on to the printing press.

There are standard punch systems used for hand-drawn animation
to holds gels in register.

For 4x5 work the standard cheap way to work is with a 2-hole
paper punch and loose pins. The negative carrier has clearance
holes drilled in to it for the pins. For 8x10, a 3-hole punch with
the center punch disabled is a standard solution.

--
Nicholas O. Lindan, Cleveland, Ohio
Darkroom Automation: F-Stop Timers, Enlarging Meters
http://www.darkroomautomation.com/index2.htm
n o lindan at ix dot netcom dot com