44/47 pretty much everywhere. Occasionally the schematic will specify a flashing bulb in the backbox, but not always. And as you've noted sometimes the socket area in the backbox will be concave for a flashing bulb. Aside from that it is really a matter of preference how blinky the owner/operator wants the backbox to be.
I like to refer to them as blinkers, because the bulbs themselves are designed to provide the blinking. This is in contrast to "flashers" in the solid state world where the CPU sends a brief pulse to special lamps to accomplish the flash effect. When one says "flasher" most picture the solid state flashlamps and CPU pulses.
Here is a sample from Gottlieb Mini Cycle:
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