Axial lead packages are through-hole electronic components whose wire leads extend from opposite ends of the body along its longitudinal axis. They are the dominant form factor for through-hole resistors, signal diodes, and many film capacitors and inductors. This guide covers standard axial package sizes across every major component type, the JEDEC and IEC designations you will encounter on datasheets, and the PCB layout and mounting rules that ensure reliable solder joints.
Key Takeaways
Axial resistor body size scales with power rating: a 1/4 W metal film body measures roughly 2.3 × 6.3 mm; a 2 W part grows to approximately 5.5 × 15.5 mm. Dimensions are not rigidly standardized—always verify against the specific manufacturer datasheet.
Axial diode packages follow the JEDEC DO-204 family: DO-35 (signal, body ≤1.85 mm dia.), DO-41 (1 A rectifier, ≤2.72 mm dia.), DO-15 (≤3.55 mm dia.), and DO-201AD (power, ≤5.08 mm dia., 10 A rated).
IPC-7251 / IPC-7252 define the land pattern rules for axial components. Drill hole diameter = maximum lead diameter + 0.20 to 0.35 mm, depending on producibility level (Level A most producible, Level C highest density).
Per IPC J-STD-001, leads must extend at least one lead diameter (minimum 0.8 mm) from the component body before the first bend. Violating this cracks the glass-to-metal seal on diodes and damages resistor end caps.
What Is an Axial Lead Package?
An axial lead package is a through-hole component housing where two wire leads exit from opposite ends of a cylindrical or rectangular body, aligned along the component’s main axis. When mounted horizontally on a PCB, the body lies flat between two plated holes. When mounted vertically, one lead goes through a hole and the opposite lead bends down into an adjacent hole, standing the component upright.
Common axial components include carbon film and metal film resistors, Zener and signal diodes, glass and film capacitors, axial-leaded inductors, fuses, and some LEDs. The leads are typically solid tinned copper wire ranging from 0.45 mm to 1.3 mm in diameter depending on the component’s current rating.
[IMAGE 1: Annotated diagram showing an axial component with body length, body diameter, lead diameter, and lead spacing labeled | alt: “Axial lead package anatomy showing body length diameter and lead spacing dimensions”]
Axial Resistor Sizes by Power Rating
Axial resistor dimensions are loosely standardized by IEC 60062 (international) and EIA RS-253 (US). Body size scales with power rating, but varies between manufacturers and resistor technologies (carbon film, metal film, wirewound). The table below gives representative ranges for modern metal film and carbon film types.
| Power Rating | Body Length (mm) | Body Diameter (mm) | Lead Dia. (mm) | Typical Pitch (mm) |
| 1/8 W | 3.0–3.5 | 1.5–1.8 | 0.45 | 7.5–10 |
| 1/4 W | 6.0–6.5 | 2.2–2.6 | 0.50–0.55 | 10–12.5 |
| 1/2 W | 8.5–9.5 | 3.0–3.5 | 0.60–0.70 | 12.5–15 |
| 1 W | 11.0–12.5 | 4.0–4.5 | 0.70–0.80 | 15–17.5 |
| 2 W | 14.5–15.5 | 5.0–5.5 | 0.80 | 17.5–20 |
| 3–5 W (wirewound) | 17–25 | 6–8 | 0.80–1.0 | 20–25 |
Sources: IEC 60062, EIA RS-253, Practical Components wattage-based naming (e.g., 1/2-W-AR-3.5×9.5 mm), and Vishay/Yageo metal film datasheets. Wirewound dimensions vary widely by construction—always verify.
Carbon composition resistors from the 1960s–1980s run significantly larger than modern metal film parts at the same wattage. A legacy 1/2 W carbon composition body may match the dimensions of a modern 1 W metal film. When replacing components on vintage boards, measure the footprint pitch before ordering.
Axial Diode Packages — DO-35 Through DO-201AD
Axial diode packages are standardized under the JEDEC DO-204 family. Each variant specifies body length, body diameter, lead diameter, and minimum lead length. The DO-204 designation is the formal JEDEC name; the original shorthand (DO-35, DO-41, etc.) remains dominant in datasheets and distributor listings.
| Package | JEDEC Name | Body Dia. (mm) | Body Length (mm) | Lead Dia. (mm) | Typical Use | Example Part |
| DO-35 | DO-204AH | ≤1.85 | 3.0–4.0 | 0.46–0.55 | Signal diodes | 1N4148 |
| DO-41 | DO-204AL | 2.0–2.72 | 4.06–5.21 | 0.46–0.55 | 1 A rectifiers | 1N4007 |
| DO-15 | DO-204AC | 2.65–3.55 | 5.85–7.62 | 0.69–0.88 | 3 A rectifiers | 1N5408 |
| DO-27 | — | 3.5–4.5 | 7.0–8.5 | 1.0–1.3 | 3–5 A power | 1N5822 |
| DO-201AD | DO-204AG | ≤5.08 | 7.2–9.5 | 1.2–1.3 | 10 A power | 10A10 |
Sources: JEDEC DO-204 family specifications, Diodes Incorporated package outlines (DO-35, DO-41 Plastic, DO-201), Vishay General Semiconductor packaging document.
Cathode polarity is marked by a painted band near one end. Vishay’s axial packaging document specifies that all axial-leaded devices are taped per EIA standard RS-296-E for automated insertion. For high-volume production, components arrive on continuous ammo-pack tape in 26 mm or 52 mm widths.
Axial Capacitors and Inductors
Axial film capacitors (polyester, polypropylene, PEN) range from 5 mm body length for low-value types (100 pF–10 nF) up to 30+ mm for high-voltage or high-capacitance variants. Body diameter typically spans 2.5–12 mm. Lead pitch matches the body length plus lead extensions, typically 7.5 mm to 27.5 mm.
Axial electrolytic capacitors exist but are less common than their radial counterparts. Axial electrolytics are preferred in military and aerospace applications where horizontal mounting and vibration resistance are required. Sprague (now Vishay) Type 150D and Type 196D are well-known axial tantalum families.
Axial inductors (molded or leaded core) follow similar dimensional patterns to resistors at equivalent power ratings. RF chokes in the 1–10 µH range commonly use a 1/4 W resistor-size body (≈6.3 × 2.3 mm). Larger power inductors may exceed 25 mm in length. Unlike resistors, axial inductors are often color-coded using the same 4-band scheme.
[IMAGE 2: Side-by-side photos of an axial resistor, axial diode (DO-41), axial film capacitor, and axial inductor with key dimensions labeled | alt: “Axial lead packages for resistors diodes capacitors and inductors with dimensions”]
Horizontal vs Vertical Mounting
Horizontal mounting is the default for axial components. The body lies flat between two PCB holes, creating a low profile (≤3–5 mm above board for standard resistors). Both leads bend 90° downward at the point where they enter the hole. IPC J-STD-001 requires that the bend start at least one lead diameter (minimum 0.8 mm) from the component body to avoid internal damage.
Vertical mounting stands the component perpendicular to the board. One lead goes straight into a hole; the other bends 180° and enters a nearby hole. This reduces footprint width from the full lead span to roughly the body diameter plus one hole pitch (~2.54–5 mm). Vertical mounting is common when board area is constrained but clearance height is available, and for higher-density automated insertion.
In both cases, IPC-A-610 Class 2 requires that the lead protrude at least 0.5 mm below the board surface (solder side) to ensure adequate barrel fill during wave soldering. Maximum protrusion should not exceed 2.5 mm to avoid interference with chassis or adjacent boards.
PCB Layout Rules for Axial Lead Packages
IPC-7251 and its substandard IPC-7252 (discrete axial and radial components) define land pattern geometry for axial parts. The three producibility levels are:
Level A (most producible): hole diameter = max lead diameter + 0.35 mm; land diameter = hole + 1.6 mm.
Level B (standard): hole = max lead + 0.25 mm; land = hole + 1.4 mm.
Level C (highest density): hole = max lead + 0.20 mm; land = hole + 1.2 mm.
For a standard 1/4 W resistor with 0.55 mm max lead diameter, Level B gives a finished hole of 0.80 mm and a land (pad) diameter of 2.20 mm. The courtyard (keep-out boundary) extends 1.0 mm (Level A) or 0.5 mm (Level C) beyond the outermost land edge.
Annular ring must meet IPC-2221 minimums: 0.15 mm for Class 2 (general commercial), 0.05 mm for Class 3 (high reliability). If your fabricator’s drill registration tolerance is ±0.075 mm, pad size must account for that drift.
[IMAGE 3: PCB footprint dimensioning diagram for a horizontal axial component showing hole diameter, land diameter, lead span, and courtyard | alt: “IPC-7251 axial lead package PCB land pattern dimensions”]
Axial vs Radial vs SMD — When to Use Each
Axial components offer flexible lead spacing (adjustable by bending), a low profile when mounted horizontally, and easy identification (color bands face upward). They are standard for automated axial insertion machines and wave soldering. Best for legacy designs, military/aerospace (where axial formats remain qualified), prototyping, and layouts where variable pitch is needed.
Radial components have both leads on the same side, occupying less board area than horizontal axial parts but standing taller. Electrolytic capacitors are predominantly radial. Radial insertion machines run faster than axial inserters in most factory configurations.
SMD (0402, 0603, 0805, etc.) achieves the highest component density and lowest profile. SMD reflow soldering is faster and cheaper at high volume. Choose SMD unless you need the mechanical strength, vibration resistance, high power handling, or field reparability that through-hole provides.
Frequently Asked Questions
What is an axial lead component?
An axial lead component is a through-hole electronic part with wire leads extending from opposite ends of its body along the same axis. Common examples include metal film resistors, signal and rectifier diodes (DO-35, DO-41), film capacitors, and molded inductors. The leads insert through holes in a PCB and are soldered on the opposite side.
What is the difference between axial and radial leads?
Axial leads exit from opposite ends of the component body in a straight line. Radial leads exit from the same side of the body, parallel to each other. Axial parts mount horizontally (low profile) or vertically; radial parts mount vertically by default and use less board area but stand taller above the PCB surface.
What size is a 1/4 W axial resistor?
A standard 1/4 W metal film axial resistor has a body length of approximately 6.0–6.5 mm and a body diameter of 2.2–2.6 mm, with 0.50–0.55 mm lead diameter. Typical PCB pitch is 10–12.5 mm. Exact dimensions vary by manufacturer—check the specific datasheet for your chosen part.
What JEDEC package is a 1N4148 diode?
The 1N4148 is packaged in DO-35 (JEDEC designation DO-204AH). The DO-35 glass body measures approximately 3.0–4.0 mm long with a maximum diameter of 1.85 mm. Lead diameter is 0.46–0.55 mm. The cathode is marked by a band near one end of the glass body.
Choosing Your Axial Package
Match the power rating to the physical size. For resistors, specify the wattage first, then verify the body and pitch fit your PCB footprint. For diodes, select the JEDEC package that accommodates your current and voltage requirements—DO-35 for signal, DO-41 for 1 A rectification, DO-201AD for 10 A power. Confirm the lead diameter against your drill file: IPC-7252 Level B adds 0.25 mm to the maximum lead diameter for the finished hole size.
Before committing to axial in a new design, ask whether SMD achieves the same function in less area. If through-hole is required for mechanical strength, rework access, or qualification compliance (MIL-PRF-55342 for resistors, MIL-PRF-19500 for diodes), axial remains the proven, readily available choice. For production volumes above 10,000 units, confirm your assembler supports automated axial insertion—not all SMT-focused lines have this capability.
