Dellorto "small" (5mm thread) jets have a slightly different thread pitch compared to the Keihin 5mm ones.
They do fit somehow, but there's a risk of twisting the head off or cracking the needle jet because of the increased resistance, so proceed with care....
_If_ (!) your needle jet survives the first few jet changes, it's adapted enough to keep using those Dellorto jets, just don't go back to Keihin type because that would stretch it the other way again, increasing the risk of failure...