Are those steel screw just part of the forming process? If they stay as part of the inductor, they may affect the final inductance slightly.
Also hoping that their black coating is insulative. And stays that way under operation.
If this is for a Tesla, is using tube even a good idea? At high frequency you will have two "skin effects" to worry about, outer layer of copper and inner layer of copper.
No it is not a tesla coil. Copper tubing works perfect for tesla coils. Refrigeration tubing is 1/2 the price of water plumbing tubing, 1/2 the weight, and it bends much easier. See attached photo with 1/4" copper tubing primary coil. 12KW outputs is a 27 foot diameter circle of 12 ft long sparks from the 3 ft diameter sphere.
I made those 40 turn coil for a certain project then after getting it made I got to thinking, wonder if anyone has a good idea for a project this coil can be used for? I like fun unusually projects. If I put the correct capacitor in parallel with this coil, and a 1N34 diode with earphone it might make a good crystal radio. LOL.
Here is my plan for this 40T coil. I am going to replace the secondary coil of a 1500w MOT = Microwave Oven Transformer with 1 or 2 turns of welding cable. I think welding cables are 400a I have not checked yet. Attach the 400a wire to both ends of the 40T coil. Connect my 1500w variac in series with 120 volts to the primary coil of the MOT. If secondary coil is 1v that will = 1500 amps. I should be able to use the variac to adjust the coil temperature to 170 degrees. If I run water through the coil it is an instant tankless hot water heater that produces 170 degree water. Camp ground electric and water is free and our camper has no hot water heater. If i set this outside on the ground and connect water through the coil to the camper we should have free hot water. If it work?