The Primary coil
The Primary coils function is to transfers the energy from the main tank capasitor in to the secondary coil, it will only need to be a few turns of VERY thick wire or in most cases thin walled copper pipe called "Micro bore".
There are a few different styles of primary coil set up  - thses are the flat primary or the cone primary, the cone shape is great for lower powerd coil setups, the flat primary can also be used to alter the coupling between the primary and secondary coils, below are a couple of pictures of different primary styles.
The next type of primary coil is the vertical helix it can be used on conventional coils but it does tend to "over couple", but is an absoulte must when building the 3 coil magnifyer system where very tight coupling is needed, again made out of 10mm copper pipe.
Pipe is used for all the primaryies because as the frequency of the AC increases the amount of the conductor that get "used" is reduced, when running at the 100`s of KHz only the very out surface of the conductor has a current flow this is called the "skin effect"
The next type of primary coil is an expermental coil design, due to space problems we needed a primary that had a lot of inductance but being space limited we came up with the double stacked primary and conical shaped, only time will tell if this type of primary works.
In the past we used to use a croc clip to attach the HV tank circuit to the primary coil but this has never been very satisfactory. I saw this idea on the Tesla mailing list. It is a common 30A 240v AC fuse holder.
The setup of a new test primary design a cup shape, the bottom turns start flat then curve up to vertical, the supports are made of Nylon 6 and it uses 8mm copper tube all mounted to the BM7 Tesla coil. 
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