kinda late to the party and im no one of mention. but i would combine the face groups inside the cylinder before converting the mesh. this should allow you to select all the contraining boundries inside as a group after you convert. so you should be able select the inside boundary of that cylinder. create a copy then push/pull to measurement, then extrude.
@@BellyUpFishGarage Thank you for the reply. I gave up trying to modify the part and just built my own with fusion. No matter how I tried I just could not get the STL file to come up without the triangles. I do want to thank you for your response. At 80 it is often difficult to get what seems simple to work.
