A Blind Tap is when a Tapped Hole Does Not go all the way Through, Such as a Round Ball. The Thread Goes Some of The Way Through. Blind Tap Threads are Common on Finials and Caps as well as Brass Balls.
Threaded Through Tapped Holes Go All the Way Through. A Nipple or a Screw can Pass All the Way Through. This is Common on Lamp Couplings and Lamp Necks.