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The 3800 uses a mix of SAE and Metric threads. Generally most things that bolt into the block internally are going to be SAE threads, most other threads are going to be metric with a few exceptions.

Block and Timing Cover

Location Thread Size, Length, and count
Main bearing cross-boltsM8x1.25 @ 50mm (6x)
Oil pan to block1/4-20 @ 1“ (20x)
Timing cover to block bolts5/16-18 @ 3.125” (6) - - @1.5“ (4)
A/C bracket and RWD Motor mount boltsM12x1.75 @ 35mm (3)
Starter motorM10x1.5 @ 50mm (1) - - @ 115mm (1)
Battery cable to blockM10x1.5 @ 20mm (1)
EGR to block3/8-16 @ 1” (2)
Engine bracket to blockM10x1.5 @ 70mm (1) - - @ 75mm (1) - - M12x1.75 @ 130mm (1)
Power steering to block (bracket)M8x1.25 @ 75mm (2)
Power bracket to block ('00+)M8x1.25 @ 80mm (1) - - @ 25mm (2)
Oil filter bracket to timing cover5/16-18 @ 1.5“ (4)
water pump bolts1/4-20 @ 1.125” (4) - - 5/16-18 @ 3“ (4)
Cam sensor bolt1/4-20 @ 5/8” (1)
Flexplate to crank (auto trans cars)5/16-18 @ (1/2“?, 5/8”?, or 3/4“?) (8)
Flywheel to crank (manual trans only)5/16-18 @ 7/8” (8)
Pressure plate to Flywheel (manual trans only)M8x1.25 @ 22mm (6)
Oil level sensor thread sizeM20x1.5
Bellhousing boltsM12x1.75 @ 45mm

Heads

Location Thread Size, Length, and count
Valve cover bolts1/4-20 @ 5/16“x5/8” shoulder (12)
Header to head bolts5/16-18 @ 1“ (9x) - - @ 1.5” (3x)
engine lift bracket to block5/16-18 @ 5/8“ (2)
Intake manifold to head bolts5/16-18 @ 1.125” (12)
EGR to manifoldsM6x1 @ 25mm (2)

Intake/Supercharger

Location Thread Size, Length, and count
Supercharger to LIMM8x1.25 @ 40mm (9) - - @ 60mm (1) - - @ 80mm (1)
SC snout to SCM8x1.25 @ 50mm (9)
Bracket to TBM6x1 @ 20mm (2)
PCV Cover to SCM6x1 @ 16mm (2)
Vac port to SCM6x1 @ 20mm (2)
SC bypass valve to SCM6x1 @ 16mm (2)
Vac Tee to SCM8x1.25 @ 20mm (2)
Fuel rail to SCM8x1.25 @ 10mm (1)
Fuel rail to IntakeM6x1 nut (4) and stud
Thermostat coverM8x1.25 @ 30mm (2)

Sensors and Electronics

Location Thread Size, Length, and count
Sensors to throttle bodyM4x0.7 @ 12mm (2) - - @16mm (4)
Ignition coil to control moduleM5x0.8 @ 45mm (6)
Cam sensor bolt1/4-20 @ 5/8“ (1)
MAP sensorM5x0.8 @ 30mm (2 or 4)
Starter solenoid enable nutM5x0.8 nut

Other Accessories

Location Thread Size, Length, and count
A/C bracket3/8-16 @ 2” (1)
Water pump pulleyM6x1 @ 12mm (4)
LIM water coverM6x1 @ 20mm (2)
PCV coverM8x1.25 @ 16mm (2)
Heater hose elbow bracketsM6x1 @ 16mm (2)
Evap Sensor bracketM6x1 @ 16mm (1)
EGR heat shieldM6x1 @ 16mm (1)
Supercharger tensioner bracket3/8-16 @ 1.5“ (1) - - @ 2” (1) - - @ 2.5“ (1)
Main belt tensioner bracketM10x1.5 @ 70mm (3)
Passenger Side trans bracket3/8-16 @ 3/4” (2)
AltenatorM10x1.5 @ 60mm (2)
A/C compressor to bracketM10x1.5 @ 60mm (3)
Lower SC idler pulleyM10x1.5 @ 25mm (1)

Most, if not all of this information has been gathered from Mattstrike's post on PBC