Centering ceiling fire sprinkler hole.
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Previously:
https://www.homemadetools.net/forum/...814#post210042
https://www.homemadetools.net/forum/...596#post209277
https://www.homemadetools.net/forum/...150#post214468
https://www.homemadetools.net/forum/...524#post209035
https://www.homemadetools.net/forum/...298#post185056