Guide · Mechanical upgrades
Prusa MK3S+ and MK4 to MK4S kits: what you keep and replace
What Prusa's MK3/S/+ and MK4 to MK4S kits reuse and add, the heatbed, PSU and xLCD checks before ordering, the Nextruder nozzle and the PSU that does not fit.
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Picks that fit
- DiamondBack Prusa Nextruder nozzle, 0.4 mm (polycrystalline diamond tip)Check price on Amazon
Short answer
Prusa sells two MK4S upgrade kits. The MK3/S/+ kit keeps your frame, PSU, MK52 heatbed and X/Y rods, and adds a new board, the Nextruder and motors; check your heatbed screws and PSU color first. The MK4 kit has separate options by xLCD version, so check that first. Prusa's MK3 PSU spare is not listed for the MK4.
Picks that fitAll picks and how to choose
- DiamondBack Prusa Nextruder nozzle, 0.4 mm (polycrystalline diamond tip)Check price on Amazon
MK3/S/+ to MK4S: what you keep and what you get
Prusa's MK3/S/+ to MK4S upgrade kit reuses the original frame, PSU, MK52 heatbed and X/Y rods and bearings. It adds a new xBuddy board, the Nextruder, motors and a 0.4 mm CHT nozzle.[1] It is a self-assembly kit, not a set of parts to swap one at a time.
Check these before ordering the MK3 kit
Prusa says the kit depends on the starting printer's configuration.[1]
| Your MK3/S/+ has | What Prusa says |
|---|---|
| A heatbed with 2+1 screws | Must be replaced |
| A heatbed with 2+3 screws | Compatible |
| A silver PSU | Needs a harness, adapter or a black PSU |
| A black PSU | Works as is |
You choose the PSU and heatbed options when ordering. Prusa also notes that early MK3s may lack a spool holder. If you are not sure which revision you own, start with identifying your printer and revision.
MK4 to MK4S: check the xLCD
Prusa says MK4 owners must check their xLCD version before ordering the MK4 to MK4S kit, because there are separate options for newer and older xLCD units.[2] The kit includes a 360° cooling fan with shroud and a brass 0.4 mm CHT nozzle. Prusa's assembly guide is titled for MK4/MK3.9 to MK4S/MK3.9S and has chapters on the Y-axis, xLCD, Nextruder and connectivity.[3]
What the MK4S is
Prusa lists the MK4S with a 250 x 210 x 220 mm build volume, a 0.4 mm brass CHT high-flow Prusa Nozzle and a 290 °C maximum nozzle temperature. Its spec table lists a Nextruder with a 10:1 planetary gearbox and a 240 W PSU.[4] The MK4S page collects the rest.
The Nextruder and the Prusa Nozzle
Prusa groups the MK3/S/+, MK3.5/S and MINI/+ as V6-type nozzle printers, and the MK4/S, MK3.9/S, XL and CORE One as Prusa Nozzle (Nextruder) printers.[5] Prusa says every MK4S, MK3.9S, MK4, MK3.9, XL, CORE One/+, CORE One L and Signature Oak it ships comes with the Prusa Nozzle installed or included.[6]
So after an MK3S+ upgrade, your old V6 nozzles do not simply carry over. Prusa says V6 nozzles can be used on Nextruder printers only with the Nextruder V6 Nozzle Adapter.[5] Prusa does not confirm MK8 nozzles work with that adapter, so do not assume any M6 nozzle fits.
Picks that fit2 products
For a spare after the upgrade, choose E3D's 0.4 mm brass Prusa Nextruder nozzle (PRUSA-MK4-NOZZLE-AS-0400); E3D lists the MK4S, MK4, MK3.9, XL and CORE One for it.
More on choosing
It is brass, so not for abrasive filaments. For abrasive filaments, the DiamondBack Prusa Nextruder nozzle in 0.4 mm has a diamond tip; Prusa lists it for the MK4S, MK3.9/S, XL and CORE One, rates it to 300 °C and says it is not high flow. On Amazon, check that 'Ships from / Sold by' shows Amazon.com or the brand.
E3D brass Prusa Nextruder nozzle, 0.4 mm (PRUSA‑MK4‑NOZZLE‑AS‑0400)
DiamondBack Prusa Nextruder nozzle, 0.4 mm (polycrystalline diamond tip)
Power supplies: what fits which printer
Prusa specifies the MK4S power supply as a 240 W unit made by Delta with Power Panic hardware.[7]
Prusa also sells a "PSU 24V 240W" assembly, and lists it as compatible only with the MK3/S/+. It is not compatible with the MK4, XL or CORE One.[8] A reseller listing has claimed MK4 fit; Prusa's own page says otherwise. Order a replacement PSU by your exact model from Prusa.
Next
Questions
Can I upgrade my MK3S+ to an MK4S?
Yes, with Prusa's MK3/S/+ to MK4S kit. It reuses the frame, PSU, MK52 heatbed and X/Y rods and bearings, and adds a new xBuddy board, the Nextruder, motors and a 0.4 mm CHT nozzle. It is a self-assembly kit.[1]
What must I check before ordering the MK3 to MK4S kit?
Your heatbed and PSU. Prusa says a heatbed with 2+1 screws must be replaced, while a 2+3-screw bed is compatible, and a silver PSU needs a harness, adapter or black PSU. You pick those options when ordering.[1]
What must I check before ordering the MK4 to MK4S kit?
Your xLCD version. Prusa offers separate kit options for newer and older xLCD units and says to check yours before ordering.[2]
Can I use V6 nozzles on the Nextruder?
Only with Prusa's Nextruder V6 Nozzle Adapter. Prusa does not confirm that MK8 nozzles work with the adapter.[5]
Does the MK3 power supply fit the MK4?
Not as a spare part. Prusa's PSU 24V 240W assembly is listed as compatible only with the MK3/S/+, and not with the MK4, XL or CORE One, whatever a reseller listing says.[8]