They're solid. Stovebolts use either a 3/16" OD tube or internal passages in the block and head for the oil supply to the rocker arms, depending on the year and size of the engine you're working on. The "oil connector" at the center of the two rocker shafts gets the oil, and distributes it to the rockers down the hollow shafts.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!