The CTRIO TTL Annex board is needed to allow encoders which operate at TTL voltage levels (0 - 5VDC) to work with the CTRIO (9-30VDC). This board contains circuits which step up the encoder's voltage so that it is within the the CTRIO's operating range.
The CTRIO TTL Annex board is approximately 1" in length, 1/2" wide, and 3/8" thick, with a mounting screw hole in the center of the board.
The CTRIO TTL Annex board is only available directly from Host Engineering. The part number for the boards is CTRIO-TTLANNEX, the price is $25 each.

We wondered why the picture for these looked a little grainy on your site. We were blown away when we had one (four actually) in hand. You can put 24 of these on a standard desktop ruler without stacking - 2 rows x 12 or 1 x 24. A US Nickel is almost 10% more area. It has the cutest little terminal strips I have ever seen and I have been doing this kind of stuff for over 40 years.
We did already order the ADC isolators, so those are going into this job instead of these little guys.
As for mounting, I am leaning toward inline and heat shrinking the whole caboodle.
So grab a dozen and just put them on your credit card! Serious! All 12 will fit on top, 2x3, with room to spare.
Disclaimer: All dimensions approximate, but I am going to have to check them later. I only have 1" x 2" worth of them to check with though.