And again thank you all very much for your comments.
… What type of material was used for the wrappings? …
Hi Scowler, the wrappings are made with threads of very strong linen (one natur and one black), normally used by traditionell shoe- or bookmakers.
I fixed them with fluid superglue.
… P.s. ich mag die einheiten auch nicht! 
well, I think this inch-standart is a cultural and historical thing, so we have to live with it.
Although I find these x/4, x/16, Xx/8 and so on not very easy - off course I was not grown up with it.
And not to forget: We are just bowyers, we don't want to shoot something to Mars …
