Note: Don't use a 1/4" drill bit to drill the holes in your Denix. Use the appropriate
smaller drill bit for a 1/4-20 tap and then tap the holes!
There is not enough room inside the Denix (or an MGC) beside the hammer for a 1/4" nut that holds the rod in place. Do use a nut in the magwell though, because the magwell's wall is quite thin.
The threaded rods and thumbnuts in the DEC kits are 1/4-20 which is the same as both 1/4" UNC and 1/4" BSW. The drill bit should be 5.1054 mm = 0.20100 inch = #7 US drill gauge (according to
this chart anyway).
The crossbar in the DEC kits is symmetric, but in the photos of the original you will see that one end is longer past one of the thumbnuts than at the other end. The crossbar was obviously facing one way in the colour pre-production photos and facing another way in the b/w post-production photos such as the ones in the Chronicles, and that could be a bit confusing if you don't know about it.
The b/w photos seem to be the ones that most builders seem to go by because they also show the paint chipping. Also, the scope looks straighter in them.
You should also know that the Denix's proportions are a few mm off here and there compared to a real Mauser C96, so there is no 100% exact position for the cross bar on a Denix. You will have to eyeball it and select the alignment of the parts that you like best.