Most inline fuse holders open by either twisting apart or pulling apart at a seam in the middle of the housing. The exact method depends on which of the three common designs you have: twist-and-pull, snap-apart, or screw-type. All three take seconds once you know the motion, but forcing the wrong technique can crack the housing or damage the fuse contacts inside.
Before opening any inline fuse holder, disconnect power to the circuit. For a vehicle, disconnect the negative battery terminal. For home electronics or marine applications, unplug the device or switch off the relevant breaker. This prevents shorts and electric shock while the fuse is exposed.
Identify Your Holder Type
Inline fuse holders sit along a wire rather than in a panel, with the fuse enclosed inside a sealed plastic housing. The three designs you’ll encounter are:
- Twist-and-pull (bayonet style): A cylindrical nylon housing, usually for glass tube fuses. The two halves lock together with a quarter-turn mechanism. These are extremely common in older vehicles and aftermarket wiring.
- Snap-apart (clamshell style): A flat or slightly rounded housing that hinges open or pulls apart at a center seam. Common with automotive blade fuses (ATC/ATO types).
- Screw-type: One end of the housing threads into the other like a bottle cap. Found on some marine, audio, and heavy-duty applications, especially for larger glass tube fuses (AGU size).
If you’re not sure which you have, look at the seam where the two halves meet. A visible twist-lock tab means bayonet. A thin line running across the middle with no tabs usually means snap-apart. Visible threads mean screw-type.
Opening a Twist-and-Pull (Bayonet) Holder
Grip one half of the holder in each hand. Push the two halves gently together to relieve pressure on the locking tabs, then twist one half about a quarter turn (90 degrees) relative to the other. You’ll feel the tabs disengage. Once unlocked, pull the halves straight apart. The glass tube fuse will be sitting in one of the two halves, held in place by spring-loaded metal contacts.
When reassembling, seat the fuse firmly against both metal contacts, push the halves together, and reverse the twist until you feel the tabs click into the locked position. Give a gentle tug to confirm it’s secure.
Opening a Snap-Apart (Clamshell) Holder
These holders are designed for tool-free access. Find the seam running across the center of the housing. Some have a small tab or lip you can press with your thumbnail. Pull the two halves directly apart with a firm, even tug. No twisting is needed.
On hinged versions, one side stays connected while the other swings open like a tiny book. Press the release tab, flip it open, and the blade fuse will be sitting in two metal clips. Pull the fuse straight out to remove it.
When closing, press the blade fuse into the clips until it seats flush, then snap or fold the housing shut until you hear or feel the click. If it doesn’t click, the fuse may not be fully seated. Push the fuse down and try again.
Opening a Screw-Type Holder
Hold the wired end of the holder steady and unscrew the cap counterclockwise. These typically take only two or three full turns before the cap comes free. The fuse sits inside the threaded barrel, held by a spring contact in the cap and a fixed contact at the base.
When replacing the fuse, drop it into the barrel, then thread the cap back on clockwise until it’s snug. Don’t overtighten. Excessive force can deform the housing or make the cap nearly impossible to remove next time.
What To Do When a Holder Is Stuck
Heat, vibration, and moisture can cause corrosion that seizes the two halves together, especially on screw-type and bayonet holders in engine bays or marine environments. If the holder won’t budge with normal hand pressure, don’t force it. Cracking the housing means replacing the entire holder.
Spray a dielectric lubricant (not standard WD-40, which can leave conductive residue) around the seam or threads. Let it soak for 10 to 15 minutes. Then try again with a gentle rocking or twisting motion. If the halves still won’t separate, use a small flathead screwdriver to carefully break up visible corrosion at the seam, reapply lubricant, and wait another few minutes before retrying.
Once you get a corroded holder open, clean the metal contacts inside with fine sandpaper or a contact cleaner before reassembling. Corroded contacts create resistance, which generates heat, which causes more corrosion. Cleaning them breaks that cycle.
Checking the Fuse Once It’s Out
With the holder open, inspect the fuse before grabbing a replacement. For glass tube fuses, hold the fuse up to a light and look for the thin metal strip running from cap to cap. A broken strip means the fuse is blown. Blackened or darkened glass is another reliable sign, caused by the metal vaporizing when the fuse tripped. If the metal strip looks intact and the glass is clear, the fuse is likely fine and the problem is elsewhere in the circuit.
For blade fuses, the metal strip is visible through the translucent plastic body. A clear gap in the strip means it’s blown. You can also check any fuse with a multimeter set to continuity mode: touch one probe to each end. A beep or near-zero reading means the fuse is good. No reading means it’s blown.
Replacing With the Correct Fuse
Always replace a fuse with one that matches the original amperage rating. Using a higher-rated fuse defeats the protection and can let a wiring fault start a fire. The rating is printed on the fuse body or stamped into the end caps.
Glass tube fuses come in several standard sizes, all with a quarter-inch diameter but different lengths. The most common are AGC fuses at 1.25 inches long and AGW fuses at 7/8 inch long. They are not interchangeable because the holder is built for a specific length. If you’re unsure, bring the old fuse to the parts store for a match.
Blade fuses are color-coded by amperage across all sizes. Red is always 10 amps, blue is 15, yellow is 20, and green is 30. The amperage is also printed on the top of the fuse in large numbers, so the color is really just a quick visual check. Blade fuses come in several physical sizes (Micro2, Mini, and regular being the most common), and you need the right size to fit your holder’s clips.
Once the correct fuse is seated and the holder is closed, reconnect power and test the circuit. If the new fuse blows immediately, there’s a short or overload in the circuit that needs to be found before you install another fuse.