The distinguishing feature of smooth line turnbuckles is that the thread is completely internalized. The result is an appearance with no visible threads which makes for an exceptionally clean design. Smooth line turnbuckles lend themselves to hand crimping in the field for two reasons. One, you can’t see crimp marks on the compression fitting because it’s hidden inside the turnbuckle body. Two, due to a 1/2” O.D. of the turnbuckle body, prefabricated assemblies would require large thru holes on the intermediate post than what you can achieve by field crimping smooth line turnbuckles.