I believe the sprocket Dave Krall needs is for Size 18 ladder chain,
which is 42 links per foot when new. The image at the link below
is the Size 18 sprockets listed in the catalog published by SDP/SI
- Stock Drive Products / Sterling Instrument
( http://www.sdp-si.com/index.php )
The pitch diameter (P.D.) for a 26 tooth sprocket, found by geometric
interpolation (ratio), is 2.36 inches. The tooth form is described
in this note found at
"The tooth profile of sprockets is relatively easy, not like gears.
No involute: just an arc. Draw the pitch circle which divides evenly
into pitch/number of teeth. Put the compass where link center would be
[at the root] and sweep the arc. Viola! (This will definitely get you
plenty close to original, if not indistinguishable."
Robbie Rhodes, MMD