The TF-1 comes in two versions. This version uses the regular eGo-t button head which is threaded and replaceable. 

The other version uses a variable voltage head that can be used at 3.3, 3.7 and 4.2 volts. 

See this link (http://www.trueman-ecig.com/TF1-battery-900mah-9-color-with-variable-voltage-metal-part.html) for the variable voltage version

Advantages of TF1 battery

• Metal part replaceable-Conventional metal part & variable voltage metal part for your choose.

• Safety- the 14500 battery inside can be took out for being charged. It has battery-reverse protection, short-circuit protection, over-charge, over-discharge protection.

• Cost-effectiveness- since battery can be took out, you only need to replace the body or the battery when it broke.

• Wide application range- the eGo-RS battery is with ego thread. So it can work with most of the atomizers in the market. Such as ce4 clearomizer, THOR CE4 clearomizers, evod clearomzier and MT3 clearomizer etc.