So every new(er) Merkel I've had so far has not been supplied with swivels, as far as I can recall except for one, which I believe was 7/8" or the metric equivalent. They have the European swivel stud, but generally ship with no swivels, or possibly they did and I just tossed them in the garbage because they weren't of the QD type.

There are two generally available modern day swivel stud sizes. Euro and American. On the Merkel they are the standard European size. The vey ubiquitous American Uncle Mike's QD swivels are too wide and the pin is too thick to fit a Merkel swivel stud. New England Custom Gun NECG has the correct Euro QD swivels. You can order them from their web site. I, myself was looking at their web site about 2 hours ago so your post was timely and it struck a chord with me. I had to order the euro swivels from them for my Merkel and Heym a few years ago after suffering the frustration of finding that none of my American slings or swivels would fit my fancy new euro guns.

There are also two generally available swivel loop sizes, the euro loop being narrower than the American.

I don't have the precise dimensions handy, but I'm sure there are several forum members far more knowledgable than I that will be happy to jump in and course correct my post.