From Vexilar
On our newer 19º and 12º Iceducers this will be stamped in the top of the transducer. If it has a blue bottom it is a Proview Iceducer. If your transducer has a red bottom it is a Tri-Beam Iceducer.
If you have an older transducer it becomes harder to tell unless you are familiar with the difference in size. Typically FL-8’s came standard with a 19º Iceducer
The first few years things were easy. It was just the Ice-Ducer. Then came the Narrow Beam and Dual Beam Ice-Ducers, and lately the 12 degree. Now things get a bit more interesting. As far as choosing the correct beam angle, read the previous article. Depending on the age, there may no markings on the Ice-Ducer to indicate which degree it is, but you can tell just by looking at it’s size.
The old standard 19 degree Ice-Ducer is 1 1/2″ in diameter and about 3″ tall. The newer style 19 has similar dimensions, but is cone shaped at the top. The 9 degree and Dual Beam, on the other hand, are almost 2 1/2″ in diameter and about 3″ tall, cone shaped at the top. The Dual Beam Ice-Ducer will have switch box in the cord. The 12 degree Ice-Ducer is about 1 3/4 inches across.
Ice-Ducers will continue to evolve. As we find better ways of doing things, you’ll see more and more changes. Also, the popularity of the Ice-Ducer has brought “copy cats” to the market, but remember, just because it hangs, doesn’t mean it’s an Ice-Ducer.
http://vexilar.com/blog/2014/08/28/choosing-a-transducer-beam-angle