Zebra ZD421 (ZD4A042-D01M00EZ) USB/Bluetooth
Zebra GK420d Replacement, Direct Thermal Label Printer 203
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What's in the box.
4 × 6 labels on Link-OS.
The ZD421d is Zebra's 4-inch direct thermal desktop printer and the replacement Zebra lists for the GK420d: shipping labels at up to 6 inches per second, Link-OS, and room to add networking later.
Heat is the ink.
The ZD421d is direct thermal: the printhead darkens heat-sensitive labels, so there is no ribbon, ink or toner. If a fingernail scratch leaves a black mark, the stock is direct thermal and ready to print.
Direct thermal suits shipping labels, receipts and short-term product labels.
Pick a label.
See what it prints.
The ZD421 takes media from 0.585 to 4.25 inches wide and 0.25 to 39 inches long. Choose a common size to see how it fits the 4.09-inch print area and how long it takes at full speed.
Dot counts are the printable part of the label (up to the 4.09-inch print width) multiplied by 203 dots per inch, rounded down. Times are the label length divided by the maximum 6 in/s; the first label after a pause takes slightly longer. Media ranges are Zebra's published specifications.
USB now. Ethernet when you need it.
This ZD421 has USB 2.0, a USB host port and Bluetooth LE for Zebra's setup app. The rear modular slot takes a field-installable 10/100 Ethernet or RS-232 serial module.
Rear panel
- Power inDC · external supply
- USB hostType-A
- USBType-B · USB 2.0
- Module slotEthernet or serial module
Our listing
- New · USB + USB host configuration
Takes the labels you already buy.
Direct thermal stock in the ranges below runs in the ZD421, including standard 4 × 6 shipping labels.
Link-OS and Print DNA.
The ZD421 runs Zebra's Link-OS with ZPL II, EPL 2 and PDF Direct, so it prints from the same systems as the GK420d it replaces.
Setup from a phone
Bluetooth LE 5 connects Zebra's printer setup app (Android and iOS). It is for setup only, not printing.
Real-time clock
Standard on the ZD421.
Field upgrades
Ethernet, Wi-Fi/Bluetooth, serial, peeler and cutter can be added later.
Drop-in for a GK420
A mounting adapter bracket fits the footprint of the GK420 and LP/TLP2824.
Works with the computer you have.
Zebra's Windows driver installs with Zebra's setup utility. Mac and Linux print through the operating system's built-in Zebra label drivers, which Zebra doesn't support.
A free USB port. A network drop only if you add the Ethernet module.
Ink, toner or ribbons.
Factory sealed, ready to print.
A New ZD421 arrives in Zebra's sealed carton, with everything Zebra packs inside it.
New stock in the original Zebra carton, never opened.
Zebra's own accessories stay in the carton, including the power supply.
The label roll, USB cable and AnyHDD microfiber cloth listed above are packed alongside.
Backed by AnyHDD's one-year warranty and 30-day returns, with free return shipping on defective items. We've supplied IT hardware to businesses since 2006.
Tech specs
As published in Zebra's documentation for the ZD421.
| Model | Zebra ZD421d (ZD4A042-D01M00EZ), 203 dpi |
|---|---|
| Print method | Direct thermal |
| Resolution | 203 dpi (8 dots/mm) |
| Maximum print speed | 6 in (152 mm) per second |
| Maximum print width | 4.09 in (104 mm) |
| Label length | 0.25 to 39 in (6.35 to 991 mm) |
| Media width | 0.585 to 4.25 in (15 to 108 mm) |
| Media roll | 5 in (127 mm) outside diameter; 0.5 or 1.0 in core; 1.5, 2 and 3 in with adapters |
| Media thickness | 0.003 to 0.0075 in (0.08 to 0.19 mm) |
| Interfaces | USB 2.0, USB host, Bluetooth LE 5 (setup app only); modular slot for Ethernet or serial |
|---|---|
| Languages | ZPL II, EPL 2, XML, ZBI, PDF Direct |
| Operating system | Link-OS |
| Memory | 512 MB flash, 256 MB SDRAM |
| Power | Auto-detecting 100–240 VAC, 50–60 Hz; ENERGY STAR certified |
| Operating environment | 40 to 105 °F (4.4 to 41 °C), 10 to 90 % non-condensing |
| Dimensions | 8.69 in L × 6.98 in W × 5.93 in H (220.8 × 177.5 × 150.7 mm) |
| Weight | 2.98 lb (1.35 kg) |
Sources: Zebra ZD400 Series spec sheet (01/2025); Zebra ZD421/ZD621 User Guide.
Questions we get asked.
Does it print 4 × 6 shipping labels?
Yes. It takes direct thermal media from 0.585 to 4.25 inches wide and prints 4.09 inches across, on rolls up to 5 inches in diameter.
Can I print over Bluetooth?
Not on this model. Its Bluetooth LE 5 connection is for Zebra's printer setup app only. Wi-Fi with Bluetooth is a factory or field-installed option.
Can I add Ethernet later?
Yes. The modular slot accepts a field-installable 10/100 Ethernet module with an internal print server, or a serial module.
How do I calibrate a new roll?
SmartCal: with media loaded, the cover closed and the status light solid green, press and hold Pause and Cancel together for two seconds and release.
Will it replace my GK420d?
Zebra lists the ZD421d as the GK420d's replacement, and offers a mounting adapter bracket so a ZD400 Series printer fits where a GK420 was mounted. It prints the same ZPL and EPL formats.
How fast does it ship?
Every order ships with tracking. Delivery options and timing are shown at checkout.
What warranty comes with it?
One year from the date of delivery. It may also be eligible for the original manufacturer's warranty, but AnyHDD's own 1-year coverage applies either way.
What if I need to return it?
If it fails in the first 30 days, you choose replacement or refund. There is no restocking fee, and refunds go back to your original payment method. If the item arrived defective, damaged, or isn't what you ordered, AnyHDD pays the return shipping; for any other reason the return label is yours to cover.
Has this ZD421 been used?
No. New units arrive in the sealed manufacturer carton, never opened. We've supplied IT hardware to businesses since 2006.
