I’m wondering if any of those who have experimented with fuse directionality have tried simply removing a fuse and then reinserting it in the same direction, but such that it is rotated through a significant angle (such as perhaps 180 degrees or so) about the axis corresponding to its length. Or perhaps simply removing it and then reinserting it without any apparent rotation.
The point to that experiment being to determine if the differences that are perceived may simply be due to minute differences in the physical contact between the fuse and the contacts on the holder. While that may seem to be an unlikely explanation for differences that may be perceived and attributed (or misattributed) to directionality, from a technical standpoint it strikes me as nevertheless being a less unlikely explanation than the essentially infinitesimal differences in various parameters that have been reported to have been measured between the two directions in a couple of papers that have been published, for example, by HiFi Tuning.
Of course, even that kind of experiment would not rule out the possibility that other effects might be in play, such as sonic differences that are sometimes reported to result from simply turning a component off and then on a few minutes later.
Regards,
-- Al