I can recommend the Duplicate X cymbal stackers, they are made by a guy in the Cleveland area who runs a drum shop named Dudley Taw. He has straight versions and tiltable ones in different heights to accomplish the stacked effect. Best thing about these is they are hand machined, rock solid and they have a split threaded insert so they screw over the lower cymbal threaded rod and tighten down on it with a set screw without any thread damage. Hand made and available only through small drum shops or direct from Taw's drum shop. The bases are set up to fit your choice of 1/4 -20 (vintage American) or the 6 or 8 mm thread patterns (most Japanese and modern).
Dudley has been through some health issues with himself and his family, so if you have some delay in getting a response please be patient, or if needed I can assist in communication, I just got a couple more of these very cool stackers in the last couple of weeks and I will be seeing him again in the next month.
Here's his website: http://www.duplicatex.com/