I order refills as an Add-On Item from Amazon. For about $7 I refill both blades. Those who say "not refillable" mostly want to sell complete assemblies.
Anyhow, there are three form factors, depending on the shape and width of the "claw" the refill slides through. If it looks Trapezoidal, that's the 7mm intermediate width.
There's Square 6mm and Square 8mm and Length is Break-to-Fit. Our Jap vehicles use 8mm square on the driver side, which is longer than the shorter passenger side blade that's 6mm square.
The E-Series uses two equal sized (length and width) blades. Form factor of the refills depends on whether the blades have are original or replacements.