In-Line Connection Box - Flex wires connection - DMM or LCR cables harness

[Kiriakos GR]

This search of my was powered by two motives.

First motive:  What is the cheapest In-Line Connection Box, which I can use to join and extend the length of a regular flex mains cable ?
(Regular connection in which mechanical stress will be minimum)

Second motive: What is the cheapest In-Line Connection Box, which I can use so to make a DIY Measuring cables harness which will not include necessarily full length of high voltage double insulated wire ( test leads wire Red/Black)  ?

For now my research ended by buying a product described as 55x35x15mm DIY Enclosure.
I did order the white version.

eBay sellers has gone wild, their pricing for a single In-Line Connection Box with screws for wire connection this is at 1.5 EUR and even so,  such a inline box this is limited to three wires application and it is incompatible for other use.

Therefore I am up to explore the 100% DIY path and to share my findings with our ITTSB Blog readers. 
Upon arrival I will demonstrate few ideas which I have about using them by pictures. 

[Kiriakos GR]

Today this topic starts to obtaining value. 

I am presenting project details of my first application.
As you may see from the pictures, there is partial compatibility regarding parts dimensions.
The height of connection rail (insulator) this it should be trimmed down, other than that detail, the plastic top cover after final wiring at both ends, this must be secured with Super-Glue.

I do consider this design as SAFE for indoor use.
If waterproofing bothers you?  Then you may use any sort of injected silicone.

My personal joy, this is that my primary prediction that such a box can be usable, it was correct.