The wire is separated into two halves to get the λ/2 radiating portion. The centre point is tied with string to arrest separation.
A better method, suggested by WB6BYU - OM Dale, is to use an underwriter's/electrician's knot.
Here's a link - http://hope.edu/academic/engineering/labs/Electricity_Lab/Figures.html .
The end insulators are scrap bakelite pieces, drilled to take the wire and string. Banana plugs are used at the rig-end.