Need some help please w/ elec cord & digital multimeter (long post, Sorry!)

[Malcolm McLeod]

So what kind of cable clamps should I have used exactly? I wasn't really happy with these but it was pretty much all I saw (or very similar) at those big box stores. If there's something better I'd like to use that.

This is simple style (not sure if it will fit your specific cord diameter). This is a bit more ($$ and function).

Edit: I've used these before, too. On control panel penetrations, they work well - - not sure how they would last on a rig like yours, as they might get tossed around???