Grills On 3¢ Washingtons On Cover

I have this off cover 3¢ Washington which I am told is an F grill Scott 94. These old (77), grill-novice eyes can barely see the grill, much less identify it. Can someone tell from this image if it is an F grill?





My difficulty brought to mind these two 3¢ Washingtons I have on cover.









I have assumed they have no grill, but perhaps I am wrong. I found John Becker's excellent 8/1/20 post on how to detect grills on covers and tried it out. I see no evidence of grills on these two covers, but I tried it on the above supposed #94, and I could clearly see evidence of the grill on the front of the stamp, which is not visible in normal light. Thanks John!

I think, but am not sure, that it is about 9mm wide, which would make it an F grill.