yes, these DO blink in syn with rear and front signals.
the hole is pretty much a rectangle.
it is aprox 2 1/4" wide and 5/8" high. [you will see in the picture] it opens [ into a semi-circle] where the plug/bulb holder piece goes in 3/4" there.
this picture will make more sense.
this picture was coutesy of the 'euro pimp' himself, steve aka mbenz
*92 400e 124.034, SOLD
*92 300e 124.030, SOLD