This is a Humminbird Flush Mount Transducer part no. XFM-9-20-P
I got it from Amazon.com
You'll need another part #TG-W to get temps (no hole needed)
The height is 4 to 4.5 inches (approx). The hole is 2 inch round. It it seems to be the standard hole in the FF industry for low power (sub 1000 watt) TXs.
Garmin and Lowrance makes theirs, with Lowrance being the most expensive.