Choosing a radial leaded fuse requires more than matching current and voltage. The body dimensions, lead spacing, lead diameter, lead length and PCB hole pattern must also fit the board. Two fuses can have similar electrical ratings but still be mechanically incompatible.
Which Dimensions Define a Radial Leaded Fuse?
A radial leaded fuse is installed through two PCB holes, so both the fuse body and its leads affect compatibility. The most important dimensions are normally shown in the series-specific mechanical drawing.
| Dimension | What It Means | Why It Matters |
|---|---|---|
| Body length | The longest horizontal dimension of the fuse body. | Determines how much board area the fuse occupies. |
| Body width or thickness | The front-to-back thickness of the package. | Affects spacing from adjacent components. |
| Body height | The maximum height of the body above its base. | Must fit below the enclosure or nearby mechanical parts. |
| Lead spacing | The center-to-center distance between the two leads. | Must match the PCB hole centers. |
| Lead diameter | The diameter of each metal lead. | Must be compatible with the finished PCB hole diameter. |
| Lead length | The lead length extending below the body. | Affects insertion, soldering and lead trimming. |
| Seating height | The distance between the fuse body and PCB after installation. | Affects mechanical stress, cleaning and airflow. |
| PCB hole diameter | The finished plated-hole diameter used for assembly. | Must allow insertion while maintaining reliable solder joints. |
How to Read a Radial Fuse Dimension Drawing
A product photograph can show the general shape, but only a dimension drawing can confirm the mechanical fit. Drawings commonly use letter symbols and maximum, minimum or typical values.
L, W, H or T
These letters commonly identify length, width, height or thickness. Always use the definitions printed on the specific drawing.
F, P or Pitch
These markings often indicate lead spacing or pitch, measured from the center of one lead to the center of the other.
Ø Symbol
The diameter symbol is normally used for lead diameter, PCB hole diameter or another circular feature.
Max., Min., Typ. and ±
Maximum dimensions define clearance needs. Tolerances must be included when designing a production footprint.
- Confirm whether all dimensions are in millimetres or inches.
- Use maximum body dimensions when checking board and enclosure clearance.
- Measure lead spacing from center to center.
- Do not estimate dimensions from a website image.
- Check whether the drawing applies to the exact series and lead option.
Body Size vs Lead Spacing vs PCB Footprint
These three terms describe different parts of the mechanical design. A fuse can have a similar body size to another series while using a different lead pattern.
| Term | Includes | Does Not Automatically Confirm |
|---|---|---|
| Body size | Length, width and height of the insulated package | Lead spacing, hole diameter or electrical compatibility |
| Lead spacing | Center-to-center distance between the two leads | Lead diameter, body clearance or solder-pad size |
| PCB footprint | Hole centers, finished hole diameter, pad diameter, keep-out area and orientation | Current, voltage, response type or breaking capacity |
Common Blue Light Radial Leaded Fuse Body Sizes
Blue Light currently offers four square miniature radial leaded fuse series in two body sizes. The table below uses the product data you provided. Lead spacing, lead diameter, lead length and recommended PCB hole size must still be confirmed from the series-specific dimension drawing.
| Series | Body Size | Response | Breaking Capacity | Rated Current | Rated Voltage | Approvals |
|---|---|---|---|---|---|---|
| 8ET Series | 8.5 × 5.0 × 4.0 mm | Time-Lag, T | 35–130 A* | 100 mA–15 A | 250 / 300 / 350 / 400 V AC | cURus, TÜV, CQC |
| 8ED Series | 8.5 × 5.0 × 4.0 mm | Time-Lag, T | 35–130 A* | 100 mA–15 A | 250 / 300 / 350 / 400 V AC | UL |
| 6EF Series | 8.5 × 8.0 × 4.0 mm | Fast-Acting, F | 35–50 A* | 200 mA–10 A | 250 V AC | cURus, TÜV, CQC |
| 6ET Series | 8.5 × 8.0 × 4.0 mm | Time-Lag, T | 35–130 A* | 100 mA–20 A | 250 / 300 / 350 / 400 V AC | cURus, TÜV, CQC, KC, CCC, PSE, VDE |
*Breaking capacity depends on the exact current rating, voltage version and series configuration. Confirm the value in the applicable product data sheet.
8.5 × 5.0 × 4.0 mm
The 8ET Series and 8ED Series use the narrower body format and both have time-lag characteristics.
8.5 × 8.0 × 4.0 mm
The 6EF Series provides fast-acting protection, while the 6ET Series provides time-lag protection in the wider body format.
How to Match Lead Spacing to the PCB
Lead spacing is the center-to-center distance between the two leads. It must match the PCB hole centers closely enough for insertion without forcing, twisting or placing continuous stress on the fuse body.
For a New PCB Design
- Read the nominal lead spacing and tolerance from the exact product drawing.
- Use the recommended footprint or PCB layout when supplied.
- Check the maximum body outline and keep-out area.
- Confirm the component height fits the enclosure.
- Verify the footprint with physical samples before mass production.
For an Existing PCB or Replacement
- Remove the original fuse without damaging the pads or holes.
- Measure the distance between the centers of the two PCB holes.
- Compare the original fuse drawing with the replacement drawing.
- Remove solder residue before judging whether the new leads fit.
- Do not measure only from the inside or outside edges of the leads.
How to Match Lead Diameter and PCB Hole Size
The finished PCB hole must accept the lead while leaving enough clearance for assembly and a reliable solder joint. The drilled hole size, copper plating and finished hole diameter are not always the same.
Insertion and Plating Risk
The lead may not enter the hole, or forced insertion may damage the lead, pad or plated through-hole.
Mechanical and Soldering Risk
Excess clearance can reduce mechanical stability and make consistent solder filling more difficult.
Do not apply one universal clearance value to every fuse series. Use the series drawing, PCB fabrication tolerances and your assembly process to determine the finished hole size.
How Much PCB Space Does a Radial Fuse Need?
A correct footprint includes more than two holes. The board layout should also reserve space for the full body, manufacturing tolerance, solder pads and nearby components.
- The maximum body length fits the available board area.
- The body width does not contact adjacent capacitors, connectors or heat sinks.
- The maximum installed height fits below the enclosure.
- The lead spacing matches the PCB hole centers.
- The lead diameter matches the finished hole diameter.
- The solder pads retain an adequate annular ring.
- The body is not forced against the PCB or held under tension.
- The fuse is separated appropriately from heat-generating components.
- There is enough space for inspection, soldering and possible service work.
Can You Bend the Leads to Fit a Different Footprint?
Small controlled lead forming may be acceptable only when permitted by the product specification and manufacturing process. It should not be used to hide a fundamentally mismatched PCB footprint.
| Practice | Risk | Better Approach |
|---|---|---|
| Bending directly at the body | Can stress the body-to-lead connection. | Use the correct footprint or an approved lead-forming distance. |
| Forcing leads into offset holes | Creates continuous mechanical stress after soldering. | Select a series with matching center spacing. |
| Repeated bending | Can weaken or fracture the lead. | Form the lead once with controlled tooling if permitted. |
| Manual correction in production | Creates inconsistent fit and assembly quality. | Correct the footprint or specify the correct lead option. |
Long Leads vs Short Leads
Some radial fuse families may be supplied with different lead lengths or packaging options. Lead length can affect automatic insertion, wave soldering, manual assembly and post-solder trimming.
Flexible Production Handling
Longer leads may suit insertion and trimming processes or allow a specified seating height, depending on the product option.
Reduced Post-Processing
Shorter leads may suit direct manual insertion or assemblies where the required final lead length is already defined.
Do not assume that every 8ET, 8ED, 6EF or 6ET product is available with multiple lead lengths. Use only the lead configuration shown in the applicable product drawing or confirmed by the supplier.
Soldering and Installation Considerations
Mechanical fit and soldering conditions should be checked together. Excessive temperature, long soldering time or mechanical load can damage the fuse even when the footprint is correct.
- Follow the series-specific soldering temperature and duration limits.
- Do not assume that a through-hole fuse is suitable for reflow soldering.
- Avoid bending or pulling the leads close to the body after soldering.
- Inspect for incomplete solder fill, tilted installation and damaged insulation.
- Confirm whether the product is compatible with the intended PCB cleaning process.
- Keep the body away from nearby components that create excessive heat.
- Check whether the fuse should sit on the PCB or remain at a specified seating height.
Can Similar-Size Fuses Use the Same Footprint?
Possibly, but similar body dimensions alone are not enough. Mechanical compatibility and electrical compatibility must be verified separately.
| Check | Why It Matters |
|---|---|
| Lead spacing | Determines whether the leads align with the PCB holes. |
| Lead diameter | Determines whether the leads fit the finished holes. |
| Body length and width | Determine clearance from nearby components. |
| Body height | Determines enclosure and mechanical clearance. |
| Lead length and seating height | Affect insertion, soldering and stress. |
| Rated current and voltage | Mechanical fit does not establish electrical suitability. |
| Fast-acting or time-lag | Response type affects startup and fault behavior. |
| Breaking capacity | The fuse must safely interrupt the available fault current. |
| Safety approvals | Equipment certification may require a particular approved series. |
For example, the 6EF and 6ET series share the stated 8.5 × 8.0 × 4.0 mm body size, but one is fast-acting and the other is time-lag. Even if their mechanical drawings match, their electrical behavior is not interchangeable by default.
Radial Fuse Size and Footprint Checklist
- Record the original fuse series and all visible markings.
- Confirm the maximum body length, width and height.
- Measure or verify the lead spacing from center to center.
- Confirm the lead diameter.
- Check the finished PCB hole diameter.
- Review the available board and enclosure clearance.
- Check lead length and seating height.
- Review soldering, cleaning and assembly requirements.
- Compare dimensional tolerances, not only nominal values.
- Verify current, voltage, response type and breaking capacity separately.
- Test the fit with actual samples before mass production.
Compare Our Radial Leaded Fuse Sizes
Use the links below to review the exact series. The product pages should be paired with the series-specific dimension drawing before the PCB footprint is finalized.
8ET Series
100 mA–15 A, 250 / 300 / 350 / 400 V AC, 35–130 A breaking capacity depending on the exact rating. Approvals: cURus, TÜV and CQC.
8ED Series
100 mA–15 A, 250 / 300 / 350 / 400 V AC, 35–130 A breaking capacity depending on the exact rating. Approval: UL.
6EF Series
200 mA–10 A, 250 V AC and 35–50 A breaking capacity depending on the exact rating. Approvals: cURus, TÜV and CQC.
6ET Series
100 mA–20 A, 250 / 300 / 350 / 400 V AC, 35–130 A breaking capacity depending on the exact rating. Approvals include cURus, TÜV, CQC, KC, CCC, PSE and VDE.
Radial Fuse Size and Footprint Articles
These supporting articles can be published later under this size and PCB footprint topic. Keep them as plain text until each page is live.
Related Radial Leaded Fuse Guides
Continue with the other selection, replacement and troubleshooting guides in this topic cluster.
Frequently Asked Questions
What dimensions should I check on a radial leaded fuse?
Check the body length, width and height, lead spacing, lead diameter, lead length, seating height and recommended PCB hole pattern.
What is radial fuse lead spacing?
Lead spacing is the center-to-center distance between the two leads. It is not the inside-to-inside or outside-to-outside distance.
Is body width the same as lead spacing?
No. Body width describes the fuse package, while lead spacing describes the center distance between the PCB leads.
How do I measure radial fuse lead spacing?
Measure from the center of one lead to the center of the other and compare the result with the exact series dimension drawing.
Can two radial fuses with the same body size fit the same PCB?
Not necessarily. Their lead spacing, lead diameter, lead length and tolerances may differ even when the stated body size is the same.
Can I enlarge the PCB holes to install a different fuse?
Do not modify the holes only for convenience. Check pad geometry, plating, mechanical strength, clearances, assembly quality and all electrical ratings before changing the footprint.
Can I bend the leads to match a different footprint?
Do not force the leads into mismatched holes. Any lead forming should follow the product specification and should avoid stress close to the fuse body.
Does a mechanical fit mean the replacement fuse is compatible?
No. Current, voltage, response type, breaking capacity, temperature requirements and safety approvals must also be matched.
Need Help Matching a Radial Fuse Footprint?
Prepare the original series, body dimensions, lead spacing, lead diameter, PCB hole centers, available height and electrical ratings. Blue Light can then help identify the closest square miniature fuse series and the drawings that still need to be checked.
Contact Blue Light
