Sonsivri

I think it is a known issue - crocodile connector is not very reliable especially when it connects to exterior parts of equipment chassis that is not intended for that. Wire moves around and crocodile slips out. You come with multimeter or oscilloscope in hand to make some tests, start from searching place to clutch a "ground", apply crocodile, find suspicious place on PCB or wire harness, tip the probe and finally discover disconnected ground.

Considering draft measurement situation I need a fast and reliable temporary ground connection as a potential reference. Just to slap a case/chassis by ground probe would be nice. No need to hold strongly - it have to release smoothly when I pull the wire. If a case is "grounded" and is made of steel - the solution is possible.

Tinned copper braided sleeve and neodymium magnet
(https://dl.dropboxusercontent.com/s/c3zsnxlnjtjz4kr/Tinned%20braided%20sleeve%20and%20neodymium%20magnet.jpg?dl=0)

Magnet inside sleeve. Before closing soldering
(https://dl.dropboxusercontent.com/s/a1g5fjewab02nyc/Magnet%20halfway%20closed%20inside%20sleeve.jpg?dl=0)

Completed terminal
(https://dl.dropboxusercontent.com/s/tzyszjxrislln8m/Magnetic%20wire%20terminal.jpg?dl=0)

Test LED with "sticky" minus
(https://dl.dropboxusercontent.com/s/vl8vzr4h73dv8b7/Test%20LED.jpg?dl=0)

Different options for simple logic probe
(https://dl.dropboxusercontent.com/s/jjweroniv3jllf5/Logic%20Probe.jpg?dl=0)

Heavier probe wire requires bigger magnet
(https://dl.dropboxusercontent.com/s/dw116aybbde0zhq/Bigger%20magnet%20for%20heaver%20wire.jpg?dl=0)

Magnetic fixing probe for multimeter
(https://dl.dropboxusercontent.com/s/2gfrekan3ox04fc/Magnetic%20fixing%20probe%20for%20multimeter.jpg?dl=0)

Application examples:
In contact with radio chassis
(https://dl.dropboxusercontent.com/s/dfywqhjtouis6eb/In%20contact%20with%20radio%20chassis.jpg?dl=0)

Ground reference from power "lighter" outlet
(https://dl.dropboxusercontent.com/s/a19ecpsdhijwsa9/In%20contact%20with%20power%20outlet.jpg?dl=0)

Actually the smaller terminal requires much less open ground surface for reliable fixing so cap could stay in receptacle
(https://dl.dropboxusercontent.com/s/9g0a69as6x3kc8v/In%20contact%20with%20lighter%20receptacle.jpg?dl=0)
"Lighter" outlet plug is an obvious option here but not nearly so universal.

It would be interesting to try a conductive (heat shrinkable) rubber coat over sleeve. But I have no such and don't know if it ever exists.

Here are several results from google searching for "magnetic probe":
Temperature probes with magnet fixing
https://oceancontrols.com.au/images/D/CMS-007_D.jpg
https://oceancontrols.com.au/images/D/cms-0171_1.jpg
http://www.yichun.com.tw/file/image/images/Magnetic%20temp%20probes_HP-202A-M12.jpg
http://static.coleparmer.com/large_images/95001_29.jpg

Magnetic Electrical Connector Set
https://d3s5r33r268y59.cloudfront.net/6333/products/thumbs/2014-01-14T20:51:03.332Z-magtrix.jpg.855x570_q85_pad_rcrop.jpg

That is a good idea, why didn't I thunk of that  :)

very good idea, I will use it! I have this problem quite often,places where you can't clip on a crocodile. Thanks for sharing.

Just found "4 mm Banana (female) Jack to 7 mm (0.276 ) diameter Magnet Adapter":
http://www.electro-pjp.com/en/fiche?nid=30494&prod=AdaMagnetD7F4&t=AdaMagnetD7F4
http://www.tme.eu/en/details/adamagnetd7-sw/probes-test-plugs/electro-pjp/adamagnetd7f4-sw/ ~5‎€
http://www.tme.eu/en/Document/167d7fd48864eb1bf09a9a6cf881acf5/ada_magnet.pdf
(http://static1.tme.eu/products_pics/a/c/7/ac706d88ae71fe18a5617ca79e87847f/91181.jpg)

http://www.tme.eu/en/details/606mg6-iec-sw/probes-test-plugs/electro-pjp/ ~8€
(http://static2.tme.eu/products_pics/0/0/9/00989c20ff1386dc386d8124ebcba1a5/8547.jpg)