cam follower types:

DT: Direct Tappet - shim under
DTs: Direct Tappet - shim on top
DTx: Direct Tappet - no shim
DTH: Direct Tappet - Hydraulic

FT: Flat Tappet (pushrod engine)
FTH: Flat Tappet Hydraulic (pushrod engine)

RT: Roller Tappet (pushrod engine)
RTH: Roller Tappet Hydraulic (pushrod engine)

RP: Radius Path (rocker arm)
RPH: Radius Path Hydraulic (rocker arm)

RPR: Radius Path Roller (rocker arm with roller)
RPRH: Radius Path Roller Hydraulic (rocker arm with roller)


camshaft types:

OHV: Over Head Valve (pushrod engine)
SOHC: Single Over Head Camshaft
DOHC: Dual Over Head Camshaft