The TO-220 package is a three-lead through-hole power outline, 10.11–10.51 mm wide on 2.41–2.67 mm lead pitch, with a metal tab that is electrically live and carries the heat out. Mount it wrong and you throw away most of the rated dissipation. This guide gives the JEDEC dimensions, the pinout rule, measured torque-versus-thermal-resistance data, and the point where two major suppliers disagree on the hole.

Key takeaways

• Per Vishay’s JEDEC-conforming outline: body 10.11–10.51 mm wide, lead pitch 2.41–2.67 mm, mounting hole 3.54–3.73 mm.
• The tab is tied to the centre lead on almost every three-lead device. Treat it as live.
• Grease alone cuts junction-to-heatsink resistance by about 0.6 °C/W; an isolator raises interface resistance by a factor of 3 to 6.
• Torque past 10 in·lb buys almost nothing, and several datasheets cap at 10 in·lb even though the application note suggests 15.
• On one die, ST rates 45 W in TO-220 and 25 W in TO-220FP — a 44% loss for an insulated tab.

What the TO-220 package is

The TO-220 package is a JEDEC through-hole power outline with three leads on 2.54 mm nominal pitch and a metal tab carrying a mounting hole. The tab is bonded to the die pad, so it conducts heat and, on most devices, current. Two-, five- and seven-lead versions share the same body.

“TO” stands for transistor outline. The number identifies a registered mechanical outline and says nothing about voltage, current or power. Vishay’s two-pin TO-220 drawing (document 95259) names the controlling reference: JEDEC TO-220AB rev. J, dated 24 March 1987.

[IMAGE 1: Front, side and rear views of a TO-220AB device with body width, lead pitch, tab thickness and mounting hole dimensioned | alt: “TO-220 package dimensions showing body width, 2.54 mm lead pitch and tab mounting hole”]

TO-220 dimensions and pinout

The table below is from Vishay Semiconductors document 95222, revision 23 February 2024, which states conformance to the JEDEC TO-220AB outline and dimensions per ASME Y14.5M-1994.

Feature	Symbol	Millimeters	Inches
Body width	E	10.11–10.51	0.398–0.414
Body height, excluding leads	D	14.85–15.25	0.585–0.600
Body thickness	A	4.25–4.65	0.167–0.183
Tab thickness	A1	1.14–1.40	0.045–0.055
Lead pitch	e	2.41–2.67	0.095–0.105
Outer lead span	e1	4.88–5.28	0.192–0.208
Lead width at tip	b	0.69–1.01	0.027–0.040
Lead width at shoulder	b2	1.20–1.73	0.047–0.068
Lead thickness	c	0.36–0.61	0.014–0.024
Lead length	L	13.52–14.02	0.532–0.552
Mounting hole diameter	ØP	3.54–3.73	0.139–0.147

Pinout. Pins 1, 2 and 3 run left to right with the marked face toward you and the tab behind. On three-lead devices pin 2 is the collector, drain or output, and it is electrically common with the tab. TO-220AC rectifiers and five- or seven-lead regulators do not follow that rule, so read the specific datasheet.

PCB hole size. At maximum material a lead measures 1.01 mm by 0.61 mm, a diagonal of 1.18 mm. A 1.3 mm plated hole passes that and lets the wider shoulder, up to 1.73 mm, act as the mechanical stop. Library footprints built around 1.0 mm holes will jam on worst-case leads.

Where vendors disagree. Vishay specifies the tab hole at 3.54–3.73 mm. STMicroelectronics specifies its TO-220 type A hole at 3.75–3.85 mm in the STP16NF06 datasheet. The two bands meet at 0.147 in and do not overlap in millimeters. A shoulder-washer bushing sized to the ST range will bind in a Vishay part, so size the bushing to the smaller figure or use a bushing-free spring clip.

TO-220 variants: AA, AB, AC, FP and the multi-lead versions

Seven designations share the TO-220 package body, and a purchasing line can carry any of them. Two are obsolete or non-JEDEC, and two are not through-hole parts at all.

Designation	Leads	What it is
TO-220AA	2	Obsolete JEDEC designation; two leads bent at right angles
TO-220AB	3	The standard: three straight leads to a specific dimensional spec
TO-220AC	2	Two leads plus tab; common on rectifiers
TO-220-5, TO-220-7	5, 7	Same body, finer pitch; regulators and switching controllers
TO-220F, TO-220FP	3	Tab moulded inside the plastic; isolated, higher thermal resistance
TO-262 (I-PAK)	3	TO-220 with the tab cut back; through-hole, no screw
TO-263 (D²PAK)	3–7	Surface-mount sibling; formed leads, no mounting hole

DigiKey’s TechForum draws the line that confuses most BOM reviews: TO-220AB is the JEDEC designation for three straight leads to a dimensional spec, while TO-220-3 is the generic catalogue name for a TO-220 body with three legs. They describe the same part. Search a distributor on the generic name; check mechanical conformance against the JEDEC name.

TO-220 mounting torque: what the measurements show

Vishay Siliconix ran the experiment most designers reason about from memory. AN827 (document 72674, 1 December 2003) mounted a SUP50N06-16L on a machined copper block measuring 4 in by 4 in by 0.75 in, held ambient at 25 °C, used an M3 screw with washer and nut, and measured steady-state thermal resistance against calibrated torque from 1 to 15 in·lb.

Torque (in·lb)	Bare, dry	With grease	Sil-Pad A1500	Bond Ply 100	Mylar + grease
1	2.00	1.32	3.36	4.45	4.21
3	1.71	1.10	3.25	4.17	4.20
5	1.64	1.01	3.20	3.91	4.11
7	1.62	0.97	3.15	3.71	4.09
10	1.60	0.92	3.08	3.58	4.05
15	1.56	0.90	2.95	3.46	3.95

All values in °C/W. Read the heading carefully: Vishay labels these Rth(j-c), but the numbers move with the interface material, so what was actually measured is junction-to-heatsink.

Three results come straight off the table. Torque above 10 in·lb is nearly free of benefit — the greased joint improves by 0.02 °C/W between 10 and 15 in·lb. Grease is worth roughly 0.6 °C/W against a dry joint, the cheapest thermal improvement available. Isolation is expensive: Mylar without grease measured 5.02 °C/W at 5 in·lb and fell only to 4.84 °C/W at 15 in·lb, the worst case in the study.

The destructive result is the one to remember. Vishay tightened until failure, and the M3 screw sheared at 26 to 27 in·lb.

The conflict worth knowing. AN827 concludes that 15 in·lb is typically adequate. Individual datasheets do not agree. Vishay’s IRF720 (document 91043) specifies 10 lbf·in, or 1.1 N·m, with a 6-32 or M3 screw. Vishay’s V20120C rectifier (document 89040) specifies 10 in·lb maximum. When an application note and a datasheet disagree, the datasheet governs the part you bought.

[IMAGE 3: Line chart of thermal resistance versus mounting torque for six interface media, 1 to 15 in·lb | alt: “TO-220 mounting torque versus thermal resistance for grease, Sil-Pad and Mylar interfaces”]

What an insulated tab costs you

STMicroelectronics publishes the cleanest same-die comparison available: STP16NF06 in TO-220 and STP16NF06FP in TO-220FP, one die, one datasheet (CD00002501, Rev 8, February 2007).

Parameter	TO-220	TO-220FP
Drain current at TC = 25 °C	16 A	11 A
Drain current at TC = 100 °C	11 A	7.5 A
Pulsed drain current	64 A	44 A
Total dissipation at TC = 25 °C	45 W	25 W
Derating factor	0.3 W/°C	0.17 W/°C
Rth junction-to-case, max	3.33 °C/W	6 °C/W
Insulation withstand voltage, DC	—	2500 V

Moulding the tab inside the plastic costs 44% of the dissipation rating and nearly doubles junction-to-case resistance. It buys 2500 V DC of isolation and deletes the washer, the bushing and the assembly step that most often produces a tab-to-chassis short.

The gap narrows once isolation is a requirement. A standard TO-220 on a grounded sink needs a thermal pad, and AN827 puts that interface at about 2.05 °C/W over grease alone at 15 in·lb. Add it to 3.33 and you sit at roughly 5.4 °C/W against the FP’s 6. The standard package’s advantage largely evaporates.

One mechanical trap: ST dimensions the TO-220FP mounting hole at 3.0–3.2 mm against 3.75–3.85 mm for the standard part. The two are not interchangeable on the same hardware.

[IMAGE 2: TO-220AB and TO-220FP side by side, rear faces visible, showing exposed metal tab against fully moulded body | alt: “TO-220 vs TO-220F package comparison showing exposed and insulated mounting tab”]

Worked example: what a TO-220 actually dissipates

Take the STP16NF06 in TO-220, bolted to an Aavid Thermalloy 5298-series extrusion that RS lists at 3.7 °C/W. Ambient 45 °C. Junction derated to 125 °C against the 175 °C limit.

Rth junction-to-case   3.33 °C/W   (ST, maximum)

Rth case-to-sink       0.50 °C/W   (Vishay IRF720, flat greased)

Rth sink-to-ambient    3.70 °C/W   (Aavid 5298)

Total                  7.53 °C/W

P = (125 − 45) / 7.53 = 10.6 W

The datasheet headline is 45 W. The assembly delivers 10.6 W. Nothing about the TO-220 package changed between those two numbers, only what it was bolted to. That gap is the entire design problem. Free air is worse: ST specifies junction-to-ambient at 62.5 °C/W, which under the same limits allows 1.3 W.

When to leave TO-220 for TO-262, TO-263 or TO-247

Need more than about 50 W in the assembly, not on paper? Move to TO-247 or TO-264. Larger tab area, lower junction-to-case resistance, and wider lead spacing for creepage at higher working voltages.

Need surface mount? TO-263, the D²PAK, is the same body with formed leads and no mounting hole. The thermal path becomes copper area and via count, so run the board-level calculation rather than assuming parity with a bolted TO-220.

Need through-hole without a screw? TO-262, the I-PAK, is a TO-220 with the tab cut back.

Need isolation in the same footprint? TO-220FP, accepting the derating above.

Running automated insertion? Check the lead-forming spec first. The shoulder dimension b2 spans 1.20–1.73 mm and is what stops the part against the board.

Five mistakes that cause field returns

1. Torquing to the application note instead of the datasheet. Applying 15 in·lb to a part specified at 10 in·lb maximum deforms the plastic around the tab and drives thermal resistance back up.
2. Sizing the shoulder washer to the wrong vendor. Design to 3.54 mm worst case, not 3.85 mm.
3. Assuming pin 2 is safe. On most three-lead parts the tab is pin 2, sitting at drain or collector potential.
4. A 1.0 mm PCB hole. Worst-case leads present a 1.18 mm diagonal. Drill 1.3 mm and let the shoulder stop the part.
5. Believing the headline wattage. Total dissipation figures are quoted at a 25 °C case. Your assembly will deliver a fraction of it.

Frequently asked questions

What does TO-220 stand for?

TO stands for transistor outline, a JEDEC package numbering series. The number identifies a registered mechanical outline and carries no information about a device’s voltage, current or power rating. Two TO-220 parts from different vendors can differ by tens of amps. The outline governs mechanical fit only.

Is the TO-220 tab connected to a pin?

Yes, on almost every three-lead device. The tab is bonded to the die pad and is electrically common with the centre lead — collector on a bipolar transistor, drain on a MOSFET, output on many linear regulators. Treat the tab as live at that node, and isolate it from a grounded heatsink or specify TO-220FP.

What is the difference between TO-220 and TO-220F?

TO-220F, also written TO-220FP or full-pack, moulds the tab inside the plastic so it is not electrically connected. On ST’s STP16NF06 pair, one die rates 45 W in TO-220 and 25 W in TO-220FP, with junction-to-case resistance rising from 3.33 to 6 °C/W. The FP version withstands 2500 V DC.

What torque should I use on a TO-220 screw?

Follow the datasheet. Vishay’s IRF720 and V20120C both specify 10 in·lb, about 1.1 N·m, with an M3 or 6-32 screw. Vishay’s own AN827 measurements show almost no thermal benefit above 10 in·lb, and in their destructive test the M3 screw sheared at 26 to 27 in·lb.

What is the TO-220 mounting hole size?

Vishay’s JEDEC-conforming TO-220AB outline gives 3.54 to 3.73 mm. ST’s TO-220 type A gives 3.75 to 3.85 mm. The TO-220FP hole is smaller again at 3.0 to 3.2 mm. Size mounting hardware to the smallest value you might receive rather than to a single nominal number.

What to do next

Designing a new board: choose the package from the assembly calculation, not the headline dissipation. Sum junction-to-case, case-to-sink and sink-to-ambient before deciding between TO-220, TO-220FP and TO-263.

Working against a grounded heatsink: specify TO-220FP if the derated rating still clears your budget. If it does not, use a standard TO-220 with a thermal pad and accept both the extra assembly step and the roughly 2 °C/W interface penalty.

Writing the work instruction: take the torque figure from the part datasheet, never from an application note, and specify a torque driver rather than “snug”.

Building the library footprint: 1.3 mm plated holes on 2.54 mm pitch, with tab clearance sized to a 3.54 mm worst-case hole.

Buying: confirm whether a line is quoted as TO-220AB or TO-220-3 before treating them as different parts. They are not.