I was looking for the dst800 paddle wheel kit part 33-540-01 and was sent 33-398-04. This pkg says w

I passed your question on to Airmar, their tech replied as follows:

"
These two kits are very similar, the difference is the paddlewheel shaft length, both kits are intended for the DST800 transducer.  The 33-540-01 kit had a shaft with a length of .865” while the shaft in the 33-398-04 kit is .845”.  The 33-540-01 paddlewheel kit was discontinued by Airmar in November of 2013.  The customer would need to measure their existing paddlewheel shaft length to determine which shaft they are utilizing.  If they are still using an old DST800 that needed the longer shaft, they may have to replace the insert to get the “newer” style insert with the shorter shaft."