Question: 

How to use the magnetic voltage probes?

Answer: 

Mounting voltage leads to bare, non insulated conductors is the most critical job when connecting measuring equipment to an electrical network.  
To make this job less risky, one can make use of so called magnetic probes, that with 4 mm shrouded connectors fit to every voltage test lead.

Magnetic probes are included in the product packages like Fluke 1738, Fluke 1748 and Fluke 1777, but are also available as an accessory.

This video shows how test leads are connected to the network with help of these probes.