Check out Transducershieldandsaver.com. Got one for my Lowrance and couldn't ask for any better. Z21.
Agree with RangerZ21, these are to fish finder trolling motor mounting what sliced bread was to eating! They prevent the transducer from being knocked out of position and having to be straightened each time you bump a stump or rock. May result in easier breakage of the transducer itself, but, hasn't happened with me, yet.