@giorgoskok, actually, 7mm top is about perfect for all scenarios.
I based my springs upon the BLF Q8’s springs, but made the bottom diameter just a bit smaller for universal compatibility with all switch board, and top a little wider for as much contact area as possible on the cell.
Wow. Amazing. So many people want these kind of springs.
I had not expected such a demand.
If there are any springs left, if any، I will give the rest to Richard at MtnElectronics and will point him to my supplier so we can get these springs all year long.
Finally, I will post some IRL picture of what the 12x9x7mm springs look like, so you have an idea.
The big spring is equivalent to the spring I have sent a diagram and measurements to the spring supplier. It is equivalent in size to the BLF Q8 spring, except that the bottom diameter will be smaller by 1mm to accommodate almost all tail caps and switch boards.
The small spring is the Fasttech Carobronze one just for comparison.
Once I get my sample of Beryllium Copper 38% IACS springs, I will compare all of the springs and compare their conductivity. If they are good, then the groupbuy will commence!
Also, if there is enough interest for the smaller driver side spring, I will ask the manufacturer to make a batch for it.
Most batteries have a large enough anode to ensure contact with the 5mm spring.
Anyway. Please change my numbers into (for now) 50 large and 40 small springs.
A thought: conical springs, well designed, can be compressed almost flat without becoming coil-bound. These ones don’t look as if they can do that. Hopefully not a problem in this application. What is the height when fully compressed ?