This is almost certainly made to fit 7x57 cartridges, the extra length and the presence of only two lugs are the starting point for the premise. A lot of these clips are unmarked and I suspect that most of these were FN production, a company that only very rarely marked its cartridge clips.
John is right in saying that the 7x57 and 6,5x55 are similar, but almost all the Swedish clips were arsenal made locally and were marked to identify them;
The only way to recognise a 6,5x55 clip, other than the markings, is that the Swedish cartridge has a slightly thicker rim than the 7x57 so whilst a 7mm cartridge will fit loosely into a 6,5mm clip, to do the opposite will be a struggle and you’d not want to strip the cartridges into your rifle in a hurry.
So if you’ve got what look like unmarked, DWM, DM or KC marked examples of these longer clips it might be worth seeing which cartridge fits best, these non-Swedish 6,5x55 ones are hard to find.