Thrash drumming is fast, aggressive, and structurally simple — Slayer, Metallica, Megadeth, Anthrax, Exodus, Testament. The vocabulary is small. The execution is brutal. A typical thrash verse runs ♩=160–200 with the right foot grinding 8th-note double bass, the right hand on hat or ride bell, and the left hand snapping the snare on 2 and 4. The genre's ear is for density: the more notes per bar without losing the backbeat, the more thrash it sounds.
Lombardo built this template with Slayer between 1985 and 1990. Ulrich modified it for Metallica's longer-form material. Today it's the foundation under any band that puts "metal" in their genre tag without further qualifier. Get these four patterns into your hands and you can play a hundred thrash songs from instruments unknown.
Exercises
The basic thrash template: hat on every 8th, snare on 2 and 4, double-bass 8ths underneath (RLRL × 2). The hand and one foot fire on every 8th — this is constant percussion, no breathing room. ♩=160 is the entry tempo; Slayer's Reign in Blood sits closer to ♩=200, but at this speed the pattern is hard enough to be useful.
The right hand moves to the ride bell. Accents on every quarter — beat 1, 2, 3, 4 — produce the bright, ringing pulse Lars puts under Metallica's chorus sections. The off-beat 8ths are softer ride-body strokes (no accent). Snare on 2 and 4. Double-bass 8ths under everything. This is the signature thrash chorus voice: bell on the quarters, body in between.
Bell on the ride with accents on 1 and 3 only (not 2 and 4 — those land with the snare and don't need the bell-shout to come through). Constant 8th-note kicks. Snare on 2 and 4. The two-and-three accent pattern on the bell is what makes a Metallica chorus feel like a chorus instead of a verse: the bell breathes on the odd beats, the snare punches on the evens, and the kick keeps the floor.
The thrash gallop. Each beat is a kick triplet shape: boom · boom-boom — an 8th followed by two 16ths. Sticking is R · L-R per beat (or R · R-L if you start with the foot you're stronger on). Iron Maiden made the gallop famous; Slayer and Lamb of God adopted it for thrash and metal-core. The trick is the gap between the 8th and the first 16th — it has to be exactly the same as the gap between the two 16ths. Otherwise it's not a gallop, just a triplet-shaped mess.