In a radial lead package, both leads exit the same face of the component body, so the part stands vertically on the board and takes a smaller footprint than an axial part. It is the standard form for aluminum electrolytic and film capacitors, TO-92 transistors, many LEDs, and through-hole tact switches. This guide gives the standard lead spacings and body sizes, the PCB footprint math, the mounting methods, and the taping standards for auto-insertion.

Key takeaways

• In a radial package both leads leave the same side; the body stands vertical, using less board area than an equivalent axial part (NASA workmanship).
• Radial aluminum electrolytics tie lead spacing to can diameter: ø5 mm uses 2.0 mm, ø8 mm uses 3.5 mm, ø10–12.5 mm uses 5.0 mm, ø16–18 mm uses 7.5 mm (Panasonic).
• Radial film capacitors follow a lead-spacing (PCM) grid of 2.5, 5, 7.5, 10, 15, 22.5, and 27.5 mm (WIMA).
• Size the PCB hole from IPC-2222: maximum lead diameter + 0.25 / 0.20 / 0.15 mm for producibility Level A / B / C.
• Radial parts are taped for auto-insertion per EIA-468 (US) or IEC 60286-2 (international): 18 mm paper tape at 12.7 mm component pitch.
• Small lead-spacing mismatches (±0.5 mm) can be taken up by bending the leads; larger ones need the correct footprint (Specap).

What is a radial lead package?

A radial lead package is a through-hole component whose two (or more) leads exit from a single face, usually the bottom, and run parallel into the board. The body then sits upright, perpendicular to the PCB. The name comes from early ceramic disc capacitors, whose leads followed the disc’s radius; it now describes any single-sided lead exit, in contrast to axial parts whose leads leave opposite ends (Wikipedia).

[IMAGE 1: a radial lead component (leads on one side, body upright) next to an axial component (leads at opposite ends, body flat) on a PCB | alt: “Radial lead component with both leads on one side beside an axial component with leads on opposite ends”]

That geometry gives radials a vertical profile and a smaller printed-wiring footprint than a lying-down axial part (NASA workmanship). It is the default package for several families:

• Aluminum electrolytic capacitors: a cylindrical can with both leads through a rubber seal at the base (Specap).
• Film and ceramic capacitors: boxed or dipped bodies on a 2-pin or 4-pin radial layout.
• Transistors and small regulators in TO-92 and similar epoxy packages.
• Through-hole LEDs, inductors, thermistors, varistors, and sealed tact switches (E-Switch).

Through-hole radials also withstand more mechanical and thermal stress than surface-mount parts, because the leads run into the board rather than sitting on a pad; that is why they persist for bulk capacitance, power, and ruggedized designs (DigiSource).

Radial vs. axial

Both are through-hole “twin-lead” parts; the choice is orientation, and it drives board area, height, and how the part is inserted.

Factor	Radial lead	Axial lead
Lead exit	Both leads, same face	One lead from each end
Body on board	Stands vertical	Lies flat
Footprint	Small, tall	Wide, low
Insertion machine	Radial sequencer / inserter	Axial inserter
Best for	Dense boards, tall clearance OK	Low-profile, height-limited
Common parts	Electrolytics, film caps, TO-92, LEDs	Resistors, diodes, axial caps, fuses

An axial part can be pressed into a radial footprint by bending one lead into a U, and a radial part can span an axial footprint by spreading its leads; both are fine on a prototype but are deprecated for production (Wikipedia).

Radial lead spacing and body sizes

Lead spacing (also pitch, or PCM on film-cap datasheets) is the center-to-center distance between the leads, and it is the first number to get right, because it sets the hole positions. Radial families use standardized values.

For aluminum electrolytics, lead spacing scales with can diameter. Miniature series from major makers share this mapping (Panasonic KA/KS):

Can diameter ø (mm)	Lead spacing F (mm)	Lead diameter ød (mm)
4	1.5	0.45
5	2.0	0.45
6.3	2.5	0.45–0.5
8	3.5	0.5–0.6
10	5.0	0.5–0.6
12.5	5.0	0.5–0.6
16	7.5	0.6–0.8
18	7.5	0.6–0.8

Can heights are separate and range widely (for example, ø8 mm bodies from about 5 mm to over 20 mm); a real part such as the Nichicon UHE 220 µF 35 V is ø8 × 15 mm on a 3.5 mm pitch (Nichicon). Very large cans (roughly ø22 mm and up, to ø35 mm+) drop wire leads in favor of snap-in or screw terminals (Specap).

For film capacitors, the body is a box and the lead spacing follows a printed-circuit grid. WIMA calls it PCM (printed-circuit module, the lead spacing at the pin exit). The standard steps are:

PCM lead spacing (mm)	Typical body	Lead diameter (mm)
2.5	Small boxes	0.5
5	e.g. MKS2	0.5
7.5	Mid boxes	0.6
10	Larger boxes	0.6–0.8
15	Larger boxes	0.8
22.5	Power boxes	0.8
27.5	Power boxes	0.8

Larger power boxes extend to 37.5 and 52.5 mm (WIMA). A representative part, the WIMA MKS2 150 nF, is a 3.5 × 8.5 × 7.2 mm box on a 5 mm pitch with 0.5 mm leads (WIMA). Ceramic disc and multilayer radials commonly use 2.5 mm or 5.08 mm (0.2 in) spacing.

PCB footprint: hole and pad size

Once the lead spacing fixes the hole positions, size the holes and pads from the lead diameter using IPC-2221 / IPC-2222, or the dedicated land-pattern standard IPC-7251.

[IMAGE 2: a radial lead footprint with dimensions for lead spacing, hole diameter, and pad diameter | alt: “Radial lead PCB footprint showing lead spacing, hole diameter, and pad diameter”]

Hole diameter follows the producibility level (IPC-2222):

• Level A (general): hole = maximum lead diameter + 0.25 mm
• Level B (moderate): hole = maximum lead diameter + 0.20 mm
• Level C (high density): hole = maximum lead diameter + 0.15 mm

Pad (land) diameter is the hole plus twice the minimum annular ring plus a fabrication allowance (IPC-2221): pad = hole + 2 × ring + allowance, with external annular ring ≥0.05 mm and allowance 0.6 / 0.5 / 0.4 mm for Level A / B / C.

Worked example. A power part with a 0.8 mm lead at Level B gives a hole of 0.8 + 0.20 = 1.0 mm, rounded up to the nearest standard drill (about 1.1 mm). With a 0.10 mm Class 2 annular ring, the pad is 1.1 + 2 × 0.10 = 1.3 mm; many designers open that to roughly 2.0 mm for a stronger joint (IPC guidance). Give wave-soldered radials the larger clearance so solder wicks cleanly up the barrel.

Mounting methods

Most radials mount the same way, but the details change with size and polarity.

• Standard vertical insertion. Leads go straight through the holes; the body seats near the board and is wave- or hand-soldered from the far side. Bend leads at the specified radius, not at the seal (NASA workmanship).
• Self-standoff / formed leads. Many electrolytics ship with kinked or crimped leads that hold the can a fixed height off the board, easing cleaning and heat relief; Panasonic markets these as “lead-formed for self mounting” (Panasonic).
• Snap-in and screw terminal. Large cans use two or more heavy snap-in pins or screw lugs instead of wire leads, for mechanical support and current (Specap). Support tall bodies against shock and vibration.
• Polarity. Aluminum electrolytics are polarized: the can marks the negative side with a stripe, and the longer lead is usually positive. Confirm the stripe against the footprint before power-up; reversed electrolytics vent.

Taping and auto-insertion

For volume production, radials are supplied on tape and fed to a radial insertion machine (a “radial sequencer / inserter”) that cuts, forms, inserts, and clinches the leads in one stroke.

The taping is standardized. In the US it follows EIA-468 (“Lead Taping of Components in the Radial Configuration for Automatic Handling”); internationally it is IEC 60286-2 (“components with unidirectional leads”). Standard radial paper tape is 18 mm wide with a 12.7 mm (0.5 in) component pitch; a 15 mm pitch is available for larger bodies (NuWay). The machine indexes the tape on sprocket holes, so the body-to-body pitch, not the lead spacing, sets the feed. On the board side, it clinches the cut leads against the pads to hold the part through wave soldering (NASA workmanship). Match the taped lead spacing and body size the machine expects, or insertion jams.

Soldering, handling, and common mistakes

Radials are forgiving, but a few errors cause returns.

• Wrong lead spacing on the footprint. A ±0.5 mm mismatch can be bent in; anything larger needs the correct pad spacing (Specap). Do not force leads and stress the seal.
• Hole too tight. Undersized holes trap flux and give weak barrels; size from the IPC rule above, then round to a standard drill.
• No vent clearance. Leave headroom above electrolytics for the pressure vent; a lid pressed against a heatsink can rupture.
• Tall part, no support. A tall can on two thin leads is a lever under vibration; add a clip or adhesive on ø10 mm+ bodies in moving equipment.
• Reversed polarity. The single most common electrolytic failure; check the stripe every time.
• Overheating the seal. Keep hand-soldering brief; radial electrolytics tolerate only a few seconds at wave-solder temperatures.

Frequently asked questions

What is the difference between radial and axial leads?

Radial leads exit the same face of the component, so the body stands vertical and takes a small footprint. Axial leads exit opposite ends, so the body lies flat and low. Radials suit dense boards and are the norm for electrolytic and film capacitors; axials suit height-limited layouts and are common for resistors and diodes.

What is the standard lead spacing for a radial capacitor?

It depends on the family. Radial aluminum electrolytics tie spacing to can diameter: 2.0 mm at ø5 mm, 3.5 mm at ø8 mm, 5.0 mm at ø10–12.5 mm, and 7.5 mm at ø16–18 mm. Radial film capacitors use a grid of 2.5, 5, 7.5, 10, 15, 22.5, and 27.5 mm.

How do I choose the PCB hole size for a radial lead?

Take the maximum lead diameter from the datasheet and add the IPC-2222 clearance: +0.25 mm for Level A, +0.20 mm for Level B, or +0.15 mm for Level C. Round up to a standard drill. A 0.6 mm lead at Level B gives 0.8 mm; a 0.8 mm lead gives 1.0 mm.

How are radial components mounted for mass production?

They arrive taped per EIA-468 or IEC 60286-2 on 18 mm tape at 12.7 mm pitch, and a radial insertion machine cuts, forms, inserts, and clinches the leads automatically. Hand assembly inserts the leads, bends or clinches them, and wave- or hand-solders from the far side.

Which way does a radial electrolytic capacitor go?

Aluminum electrolytics are polarized. The can is marked with a stripe on the negative side, and the longer lead is normally positive. The negative lead goes to the marked pad. Installing one backwards makes it heat, vent, and fail, so verify the stripe against the footprint before applying power.

The bottom line

Pick the lead spacing first: read it from the datasheet, match it to a standard value (electrolytics scale with can diameter; film caps sit on the 2.5–27.5 mm PCM grid), and place the holes on that pitch. Size the holes from the IPC-2222 lead-diameter rule and open the pads for a clean wave-solder fillet. For volume, order parts taped to EIA-468 or IEC 60286-2 and confirm the insertion machine handles that lead spacing and body size. Mind three things every time: polarity on electrolytics, vent clearance above the can, and mechanical support for tall bodies in anything that moves. Reach for axial parts instead only when board height is the binding constraint.