I agree with all the others. That is not a Model A horn. I have never seen an "A" horn with external connections. They have similar internal connections as in the picture posted by Bob C. While the "A" horns were made by several different manufactures they all had a similar profile. While the front of your horn is not shown, what can be seen does not seem to fit the correct profile, and the mounting bracket is not Model A it looks home made.
Attached are two factory photos of very early Tudor Sedans (notice the open front bumper on the 1st "A"), the second "A" is also a very early "A" they both clearly show the profile of the early horn and that it is similar to other "A" horns.