These are generally to make holding smaller locks more comfortable or ergonomic. There are holders for an array of standardized lock profiles I have access to. Most of them will accept an 18-8 hex nut and retaining bolt, not sure what the metric equivalent is. I personally used the following parts:
18-8 Stainless Steel Narrow Hex Nut, 6-32 Thread Size
https://www.mcmaster.com/90730A007
Steel Spade-Head Thumb Screws, 6-32 Thread Size, 1" Long
https://www.mcmaster.com/90181A153
The author marked this model as their own original creation.