The IEC Photogate Kit contains 2x universal Photo Gates with all the cables and plugs required for connecting them to a digital Timer. 
The optional IEC Timer 4064101 is the recommended model, although several types of IEC Timers perform well. 

The Gates are supplied with special legs that can be pushed firmly into the sides of the Gates to permit them to engage firmly to the outer corners of the normal triangular Air Track so the Gates become integral with the Track and can be slid along the track to any position.