A bell-hole is a term for the extra working room which is excavated in a ditch to allow access and welding of a tie-in weld, sleeve etc.
An Arkansas bell-hole is an old term for a 6G pipe test. I cut my teeth in pipeline inspection in the 1970's and haven't heard that expression in 20 years. I hope someone can come up with the origon.
5G is called a bellhole, as was said, because that is the position of the pipe in a regular old bellhole weld. Once you get into the Ozark mountains tho, a regular bellhole becomes a thing of the past as you are either going uphill or downhill, hence, Arkansas bellhole equals 6G.
As was posted earlier, a bellhole is a place in the ditch that's been widened to make room to weld.
JTMcC.