bach bass trombone stradivarius model 50b (on right in pics) with "f" attachment # 3125 vincent bach new york 1967. stradivarius 50bg vincent bach elkhart (on left in pics) indiana with double keys. sold as a set. slide fits both bells. coret music co. in east meadow, ny assessed the instrument in 1971 - "in my opinion this insturment is irreplaceable" the new york bach 50b with the serial #3125 was made at the bach factory in new york in either 1947 or 1948. the 67 on the bell were the last two digits of the zip code for the bach factory on 216th street in the bronx, new york. the other bell is an early elkhart bell from the late 60's or early 70's. diameter of bell: mt. vernon 9.75 inches. indiana 9.5 inches. pictures by email.