I was recently looking at the website of an online spare parts retailer and shiny stuff caught my eye. They had for sale after market portafilters that were quite a bit fancier than the basic one on the Silvia.
My Silivia is now around 7 years old and I've well and truly got my return on investment, so spending a little bit of money on a fancy portfilter doesn't seem like a big expenditure.

The portafilters I was looking at listed a range of brands they were compatible with, with Rancilio not being one of them. Which made wonder before I go and buy anything are they a standard fitting? I've done some searching on line and can find little to no reference to using after market portafilters on a Silvia. I found one post suggesting someone had used one successfully. But another hinted that they may not be a standard fitting and that a non-original did not fit properly but it was not clear.

So long story short, is the locking thread on the Silvia portafilter a common size/design that is compatible with other brands? Have you used a non-genuine portfilter on a Silvia successfully?