DOHC engines have 24 lifters. Lifters, also known as "lash adjusters", come in 2 important varieties: Pre-1999 Lifters and 1999 (3rd Generation) Lifters.
These lifters cause a common problem known as "lifter tick". An incessant, yet generally harmless ticking from the engine bay.
1999 (3rd Generation) Lifters
These lifters are a common drop-in upgrade for the pre-99 DOHC engines.
Links: Stealth316.com has an excellent word document on the process of replacing the lifters. It can be found here Word Document: Replacing Lifters 1.8mb