The TO-8 package is a hermetic metal can roughly 15 mm across the header, taller and wider than a TO-5 and one size below a TO-3. JEDEC’s replacement designation is TO-233. It carries anything from 2 to 16 leads, which is why two parts marked TO-8 can have nothing in common but the cap. Below: the min/max outline, the thermal numbers, and where engineers still specify it.

Key takeaways

• TO-8 names a header family, not a single drawing. Lead count, cap height and lead pitch all vary within it.
• Microsemi’s 2N1483 series gives the only published min/max outline table in general circulation: cap 11.28 mm to 13.31 mm, header 13.97 mm to 16.51 mm.
• The case convention flips between parts. A 2N1483 has the collector welded to the case; an LH0033 has the case electrically isolated.
• Free-air thermal resistance is about 100 °C/W either way, but junction-to-case runs 7 °C/W for a 3-lead transistor and 60 °C/W for a 12-lead hybrid in the same can.
• The volume applications today are pyroelectric gas and flame detectors and TEC-cooled laser diodes, not transistors.

What is a TO-8 package?

The TO-8 package is a hermetically sealed metal can for semiconductors, standardized by JEDEC as one of the transistor outline drawings and superseded by the TO-233 header family. A typical TO-8 has a 15.24 mm base diameter, a 12.29 mm cap diameter and a 7.62 mm cap height, with leads on a 7.16 mm pin circle. It was designed for medium-power transistors and is now used mostly for sensors, hybrid ICs and laser diodes.

[IMAGE 1: size comparison photo of a TO-8 can beside a TO-5 and a TO-18, all three standing on a millimeter scale | alt: “TO-8 package metal can size comparison with TO-5 and TO-18”]

Three-lead TO-8 outline, with tolerances

Most reference pages quote a single set of typical numbers. Microsemi’s 2N1483 through 2N1486 datasheet (T4-LDS-0299, Rev. 1, 29 July 2013) publishes the lettered table with limits, which is what a footprint actually needs.

Symbol	Feature	Min	Max
HD	Header (base) diameter	13.97 mm	16.51 mm
CD	Cap diameter	11.28 mm	13.31 mm
CH	Cap height	6.86 mm	8.38 mm
J	Lead-circle related dimension	3.45 mm	3.71 mm
LD	Lead diameter	0.69 mm	0.84 mm
LL	Lead length	9.14 mm	11.18 mm
Q	Body-to-seating-plane offset	—	2.92 mm

Table 1. Three-lead TO-8 outline limits, per Microsemi 2N1483–2N1486 datasheet T4-LDS-0299 Rev. 1.

The header tolerance alone spans 2.54 mm. A clamp, socket or shield designed against a 15.24 mm nominal can will not hold every conforming part. Microsemi also notes that lead diameter is measured beyond 1.27 mm from the seating plane, so a caliper reading taken at the glass seal will not match the drawing.

Why “TO-8” on a datasheet tells you almost nothing

The designation drifted. Manufacturers apply it to any can with the TO-8 cap diameter regardless of lead count, and sometimes to any can of that diameter regardless of cap height. Three published variants make the point.

Variant	Leads	Cap diameter	Cap height	Lead pitch or circle
3-lead transistor (Microsemi 2N1483 series)	3	11.28–13.31 mm	6.86–8.38 mm	7.16 mm pin circle
12-lead can (EESemi)	12	14 mm	7.1 mm	2.5 mm pitch
16-lead can (EESemi)	16	14 mm	5 mm	1.91 mm pitch

Table 2. Published TO-8 variants. Cap height and lead pitch both change with lead count.

For four leads or fewer, the leads sit on a circle. Above four, they are usually arranged along the edges of a square with a 10.16 mm side, and the cap diameter grows to 13.97 mm. Interfacebus describes the 12-lead version as two vertical and two horizontal rows, with a small standoff bump under each terminal that keeps the can off the board for airflow and to protect the laminate from a hot case.

Practical rule: treat the TO-8 marking as a bin, then pull the vendor’s own outline drawing. The 12-lead part is also catalogued under the package code MBCY12 in distributor descriptions of the LH0033CG, which is a more specific search term than TO-8.

[IMAGE 2: overlay drawing of the 3-lead circular lead pattern against the 12-lead square ring on a 10.16 mm side, both on the same header outline | alt: “TO-8 package lead patterns, 3-lead pin circle versus 12-lead square ring”]

Thermal behavior: same can, very different heat paths

This is the number most TO-8 pages omit entirely. Two current datasheets, same outline, different construction.

Device	Leads	Rated dissipation	RθJA	RθJC	TJ max
2N1483–2N1486 NPN (Microsemi T4-LDS-0299)	3	1.75 W at TA = 25 °C; 25 W at TC = 25 °C	100 °C/W	7 °C/W	200 °C
LH0033 / LH0033C buffer (Calogic, package H12A)	12	2.2 W	100 °C/W	60 °C/W	175 °C

Table 3. Thermal limits for two TO-8 devices. The free-air path is package-dominated; the case path is not.

Free-air performance is nearly identical because the can and lead set dominate. The case path is not: the transistor die is soldered to the Kovar header, while the hybrid sits on an internal substrate. Bolting an LH0033 to a heatsink buys roughly an eighth of the improvement that bolting a 2N1483 does.

Worked example, LH0033C at ±15 V. Quiescent dissipation is (V+ − V−) × supply current, or 30 V × 22 mA = 0.66 W. At 100 °C/W in still air that is a 66 °C junction rise, which brackets the datasheet’s own warning that no-load junction temperature runs 40 °C to 60 °C above ambient. At TA = 70 °C the free-air budget is (175 − 70) ÷ 100 = 1.05 W, less than half the 2.2 W absolute maximum. Reaching 2.2 W requires holding the case at 43 °C.

One datasheet trap worth flagging. The Microsemi derating notes read 0.010 mW/°C and 0.143 mW/°C. Those units are wrong: 1.75 W spread over a 175 °C span is 0.010 W/°C, and 25 W over the same span is 0.143 W/°C. Read them as watts per degree or the part looks a thousand times more fragile than it is.

TO-8 against the neighboring cans

Attribute	TO-8	TO-5	TO-18	TO-66
JEDEC replacement family	TO-233	TO-205AA	TO-206AA	TO-213
Shape	Round can	Round can	Round can	Diamond flange
Base or flange size	13.97–16.51 mm dia.	8.9 mm dia. typ	5.6 mm dia. typ	31.4 × 19.0 mm
Cap diameter	11.28–13.31 mm	8.1 mm typ	4.70 mm typ	—
Cap or total height	6.86–8.38 mm	6.3 mm typ	4.83 mm typ	8.63 mm max
Pin circle	7.16 mm	5.08 mm	2.54 mm	—
Lead count range	2 to 16	3 to 10	2 to 8	3
Heatsinking	Press-on clip or clamp	Press-on clip	Press-on clip	Two screws, 23 mm centers

Table 4. TO-8 against the cans it is most often confused with or migrated to.

The selection logic follows the flange. TO-8 gives the largest cavity available without moving to a bolt-down flange, which is exactly what a four-channel filter stack or a laser-plus-TEC assembly needs. If the design is a single power transistor that must shed real watts, TO-66 or TO-3 wins because the mounting hardware, not the can, sets the case temperature.

Where TO-8 is still specified in 2026

Pyroelectric detectors are the largest current use. InfraTec builds its multi-channel gas and flame detectors in what it calls a TO8 housing at 15.2 mm diameter, up to eight measuring channels in one can. The four-channel LRM-244 puts an 8.5 mm by 8.5 mm aperture window in the cap with 2.8 mm by 2.8 mm channel filters mounted inside, and the family specifies channel crosstalk below 0.1%.

Laser diodes are the second. Photodigm’s TO-8 DBR package holds the laser, a thermoelectric cooler, a monitor photodiode and a thermistor in one header, with the option of hermetic sealing. Its test fixture datasheet (T8-1000-2A) states that heat leaves through the bottom of the TO-8 header, that thermal grease is required, and that the header tab keys into a notch on the mount.

High-reliability discretes are the third. The 2N1483 through 2N1486 series remains JEDEC-registered and available at JAN and JANTX levels per MIL-PRF-19500/180, with RoHS versions offered on commercial grade only.

[IMAGE 3: four-channel pyroelectric detector in a TO-8 can, cap window facing the camera, beside a TEC-cooled laser diode in the same outline | alt: “Modern TO-8 package uses: multi-channel pyroelectric detector and TEC-cooled laser diode”]

Mounting, footprint and assembly

Three constraints matter more than the hole pattern.

Heat leaves through the header, not the cap. Photodigm’s fixture applies thermal grease to a slot under the header. A clip-on cap heatsink helps free-air parts, but a clamped header is what moves watts.

The tab is the index. On a TO-8 with more than four leads the tab identifies lead 1; on Photodigm’s package it also mechanically keys the part into its mount. Rotational errors are silent until power-on.

Lead handling is unforgiving. The Calogic LH0033 datasheet allows 300 °C for 10 seconds at the lead. TO-8 leads pass through glass seals, and the Photodigm fixture guide explicitly warns against forcing or bending pins during insertion. Where a laser die is inside, short the diode pins before insertion.

For hole sizing, the 0.84 mm maximum lead diameter on the 3-lead outline suggests a 1.1 mm finished hole. Multi-lead variants use thinner leads on 2.5 mm or 1.91 mm pitch, so size from the specific drawing rather than the family.

Materials, screening and compliance

Microsemi specifies a hermetically sealed Kovar base with a nickel cap, and terminals of Alloy 52 with nickel plating and a Sn63/Pb37 hot solder dip, or matte tin where RoHS compliance is required. That combination matters twice: Kovar matches the thermal expansion of the glass seals, and the tin-lead option means a JAN part and its RoHS counterpart are separate order codes.

Hermetic construction also changes the qualification path. The screen that matters is a seal test, not the moisture-sensitivity handling written for molded plastic. For military grades, MIL-PRF-19500 slash sheets carry the device-level requirements, /180 in the case of the 2N1483 family.

Sourcing reality

TO-8 is a specialty package now, and pricing reflects that. The LH0033CG is still stocked as a 12-pin TO-8 metal can and is now carried under Texas Instruments’ part number following the National Semiconductor acquisition, with distributor descriptions using the MBCY12 package code. Discrete TO-8 transistors survive mainly as military-grade inventory rather than catalogue items.

Two habits protect a build. Buy through authorized distribution rather than surplus channels, because a plain metal can is trivial to re-mark and holds no molded date-code detail. And record the exact vendor and revision of the outline drawing in the footprint library, since header diameter varies by 2.54 mm across conforming parts.

For new designs, the practical second source is a different package rather than a different vendor. Pyroelectric detector families offer TO-39 and TO-46 housings with fewer channels, and laser diodes are available in TOSA and butterfly packages, so the migration path trades channel count or fiber coupling instead of hunting for another TO-8.

Design mistakes that cause returns

1. Copying a footprint from a TO-8 drawing without checking lead count, pitch and cap diameter for that specific part.
2. Assuming the case is isolated. The 2N1483 series ties the collector to the case; the LH0033 does not.
3. Sizing thermal margin from free-air numbers on a heatsinked part, or from case numbers on a part with 60 °C/W junction-to-case.
4. Designing a clamp against the 15.24 mm nominal header rather than the 16.51 mm maximum.
5. Reading the derating note literally where the units are misprinted.
6. Bending or forcing leads at the glass seal during insertion, which opens a slow leak that passes final test.

Frequently asked questions

What is a TO-8 package?

A hermetically sealed metal can package standardized by JEDEC, superseded by the TO-233 header family. Typical dimensions are a 15.24 mm base, a 12.29 mm cap and a 7.62 mm cap height, with leads on a 7.16 mm pin circle. It houses medium-power transistors, hybrid ICs, pyroelectric detectors and laser diodes.

How many pins does a TO-8 package have?

Between 2 and 16, depending on the device. Up to four leads sit on a circle; above that they are arranged along the edges of a square with a 10.16 mm side. Published 12-lead cans use 2.5 mm lead pitch and 16-lead cans use 1.91 mm.

What is the difference between TO-8 and TO-5?

Size and lead count. A TO-8 cap runs 11.28 mm to 13.31 mm across against roughly 8.1 mm for a TO-5, and the pin circle is 7.16 mm against 5.08 mm. TO-8 accepts up to 16 leads and a much larger internal cavity, which is why sensors and hybrids use it.

Is TO-8 the same as TO-233?

TO-233 is the JEDEC outline intended to replace the older TO-8 definition, covering the 0.280 in pin-circle header family. Parts are still marked and sold as TO-8, so treat the two designations as the same family and take dimensions from the manufacturer’s drawing.

How much power can a TO-8 package dissipate?

It depends on the device inside, not the can. A 3-lead 2N1483 transistor is rated 1.75 W in free air and 25 W with the case held at 25 °C. A 12-lead LH0033 hybrid in the same outline is rated 2.2 W, limited by a 60 °C/W junction-to-case path.

What to do next

If you are qualifying a sensor or a TEC-cooled laser, the TO-8 package is the right envelope and the header is your heat path. Design the mount to clamp the header with grease, key the tab, and budget from junction-to-case, not free air.

If you are recreating a legacy board, identify the exact device before touching the footprint. Pull the vendor drawing, confirm lead count, pitch and whether the case is a terminal, and size the clamp against the maximum header diameter rather than the nominal.

Primary sources

• Microsemi 2N1483–2N1486 datasheet (TO-8 outline table, thermal, MIL-PRF-19500/180) — https://www.micro-semiconductor.dk/datasheet/9a-JANTX2N1485.pdf
• Calogic LH0033 / LH0033C datasheet (package H12A, 12-lead TO-8) — https://www.tvsat.com.pl/pdf/L/lh0033cg.pdf
• Photodigm T8-1000-2A TO-8 laser diode package test fixture datasheet — https://www.photodigm.com/wp-content/uploads/2023/09/T8-1000-2A-Data-Sheet-08222023.pdf
• InfraTec multi-channel pyroelectric detectors (TO8 housing) — https://www.infratec-infrared.com/sensor-division/multi-channel-detectors/
• JEDEC Publication 95 transistor outline index — https://www.jedec.org/sites/default/files/TOINDEX.pdf

Proposed internal links

• [INTERNAL LINK: “TO-5 and TO-39 metal can packages” → TO-5 package reference page]
• [INTERNAL LINK: “TO-72 four-lead metal can” → TO-72 package reference page]
• [INTERNAL LINK: “hermetic packaging and seal testing” → package hermeticity and MSL explainer]
• [INTERNAL LINK: “thermal resistance and derating basics” → junction-to-case thermal design guide]
• [INTERNAL LINK: “sourcing obsolete discretes safely” → component authentication and sourcing guide]