Mine are fastened with the square hole Robinson screws.
X2. IIRC from when I relocated my '02 C190's rear door curtains, they take a size 0 driver. I think the only one I found locally was in a set of various driver bits from Home Depot. But that's dredging up a maybe-memory from 8-9 years ago.
Jim, "Talk nerdy to me."
'06 Tiger CX 'C Minus' on a Silverado 2500HD 4x4, 8.1 & Allison (aka 'Loafer's Glory') www.tigervehicles.com