DC Plug Adapter Set, 5521 5525 4017 3513 2.5mm

Q: What is the minimum order?

Prototypes start at 5 sets and ship in 3 working days. Production runs start at 500 sets and ship 14 working days after sample approval.

Overview

A power adapter that almost fits is a power adapter that does not work, and barrel connectors are built to be confused: the outside diameters
repeat across sizes while the pin diameters differ by fractions of a millimeter. This DC plug
adapter set covers the six barrel sizes that
account for most of that confusion, so an installer can make the connection on site instead of
reordering and returning the next day. Every piece is molded, marked with its size, and center
positive, so the polarity is visible before anything is plugged in.

Key Specifications

Set contents	6 molded socket-to-plug barrel adapters
Sizes covered	5.5×2.1mm, 5.5×2.5mm, 4.0×1.7mm, 3.5×1.35mm, 1.35mm, 2.5mm
Rated voltage	24 VDC maximum
Rated current	Up to 5 A per adapter
Contact material	Nickel plated brass
Polarity	Center positive, marked on each piece
Body	Molded insulation, size printed on each adapter
Applications	Routers, cameras, single-board computers, LED drivers

Barrel size reference

The two numbers on a barrel connector are the outside diameter of the plug and the inside diameter
of the socket pin, in that order. The short codes below are trade shorthand rather than a formal
standard, and two suppliers can use the same code for slightly different parts — measure the actual
connector before you rely on the code.

Code	Plug OD x pin ID	Commonly found on	Notes
5521	5.5 x 2.1 mm	Routers, CCTV cameras, LED strips, compact satellite terminals	The default in low-voltage DC; the one most adapters convert from
5525	5.5 x 2.5 mm	Laptop-style supplies, some monitors, portable tools	Same outer shell as 5521, so a 5521 plug rattles in it
4017	4.0 x 1.7 mm	LED drivers, small printers, compact consumer gear	Often mistaken for 5521 at a glance; measure it
3513 / 35135	3.5 x 1.35 mm	Compact network gear, hubs, some single-board computers	1.35 mm is the pin size on this family, which is why it is listed both ways
2.5 mm	2.5 mm sub-miniature plug	Small cameras, older consumer electronics	Shares dimensions with the 2.5 mm audio plug, which is why it is easy to mis-order
1.35 mm	1.35 mm pin family	Micro barrel inputs on compact devices	Usually paired with a 3.5 mm outer barrel

How to measure a barrel connector

Measure the socket pin, not the hole. The outside diameter is the same across
several sizes, so the outer measurement rarely tells you what you need. A caliper on the center pin of
the socket gives the second number.
Measure the plug you already have. Outside diameter across the barrel, then the
hole in the end if you can get a pin gauge into it.
Check the label. Most supplies print the output plug size, or at least the
voltage and current. A 12 V 1 A supply is not going to be on a 1.35 mm micro barrel.
Test the feel. A plug that enters but feels loose, or a device that powers
intermittently, means the inner diameter is wrong, not the outer.
Check polarity last. Center positive is the convention, and it is marked on each
adapter in this set, but check the symbol on the device too.

Where a set earns its keep

Service vans and field engineers, where the fix has to happen on the first visit
CCTV and access control installers mixing camera brands on one site
Rack and bench builds where the supply and the load came from different vendors
Spares kits shipped with an appliance, alongside a DC barrel adapter kit
Distributor counter stock, bagged under your own part number

Ratings, limits and what not to do

Each piece in this set is a low-voltage DC part. The voltage and current limits your set is built
and verified to are the values stated on your drawing — we do not publish figures beyond that, and the
ratings on an existing listing are not a substitute for the drawing on a new order. Three rules apply
whatever the numbers:

Mains voltages are out. These are low-voltage DC parts and nothing else.
Do not stack adapters more than one deep. Every added joint costs a little voltage and adds a point of failure, and a stack of two is a lever waiting to snap a socket off a board.
An adapter does not fix an undersized supply. If the supply cannot deliver the current, changing the plug will not change that.

The contacts are nickel plated brass, which seats firmly and holds up to repeated insertion better
than a bare stamped sleeve, and each body is molded with the size printed on it so the set does not
turn into a bag of lookalikes after the first job.

Typical applications for this DC plug adapter set

Connecting a 5.5×2.5mm supply to 5.5×2.1mm gear, the single most common mismatch on site
Feeding 4.0×1.7mm LED drivers from a standard 5.5×2.1mm rail or battery box
Bringing compact 3.5×1.35mm network gear onto a shared 12 V distribution panel
Covering the 2.5 mm and 1.35 mm sizes on older or imported equipment
Extending a sealed run first with our IP67 waterproof DC extension cable, then adapting at the load

How to specify your order

Which sizes — the standard six, or a set built around the two or three you actually see.
Contact plating — nickel plated brass is stock.
Marking — size printed on each piece, plus your part number if you want it.
Packaging — bagged as a set, boxed, or individually bagged for counter sale.
Quantity, and whether samples are needed first.

Workmanship and testing

IPC/WHMA-A-620 Class 3 is the workmanship bar for DC Plug Adapter Set builds, and ISO 9001 is the system behind the line, from 32 to 12 AWG. No DC assembly is boxed before continuity and pinout are confirmed, and seal checking is quoted whenever an ingress rating is on the drawing.

Material declarations against RoHS and REACH are issued per project, alongside the dimensional and electrical reports agreed at quotation; see certifications, compliance and material declarations. Where your drawing names a UL style or another approval, the build follows your drawing and ships with the supporting document rather than a claim of our own. Overmold tooling for this part is designed and cut in our own tool room under overmold tooling cut in our own tool room, so the tool belongs to your program and a revision is a machining job rather than a new negotiation. More background: our marine and outdoor work.

Related barrel adapters and leads

Full range: DC Plug Power Cable.

Frequently Asked Questions

How do I know which insert I need?

Measure the center pin of the socket with a caliper. The outside diameter is the same across several sizes, so the pin measurement is the one that identifies the part.

Are these center positive?

Yes, every piece in the set, and each one is marked so the polarity is visible before you plug anything in. Check the device symbol as well.

Can I stack two adapters?

We advise against it. Each joint adds resistance and a mechanical lever on the socket; use one adapter or order the correct plug.

Will an adapter let me use a higher voltage supply?

No. It changes the plug, not the supply. Match the voltage on the device label.

What is the minimum order?

Five pieces is the prototype minimum for DC Plug Adapter Set builds, shipping in 3 working days. The production minimum is 500 sets, delivered 14 working days after sample approval.