The last two 1604290 (35mm) drum supports I have used have come without the holes for the bolts threaded.
I have had to use a thin, round file on the top of the hole to allow me to get the bolt started but it is a real pain and is likely to break the odd torx bit due to the pressure needed to cut the thread with a new bolt. 🙁
Yup .. mine too… I have never had one that was not threaded and would have sent it back if I got one in that condition..
That’s why I asked if it was an original or a spurious one.