N42 Neodymium Disc Magnets — 4 x 3 mm
Nickel-Copper-Nickel coated • Axially magnetised • Packs of 1, 10, 25, 50 and 100
The most holding force available from a 4 mm hole. 450 g of pull for heavy metal parts and jobs where the bore is already fixed.
Why this size
✓ Maximum pull from a 4 mm bore. 450 g — the strongest disc we stock at this diameter. When the hole width is dictated by the part and 4 x 2 mm is not enough, this is the answer.
✓ Calculated pull: 450 g at direct contact. Zero gap, clean flat steel. Magnet-to-magnet also 450 g. Reference value, not a guaranteed working load.
✓ Enough for white metal. Cast metal barrels, weapon arms and heavy resin assemblies stay seated through handling and transport, not just on the shelf.
✓ Deep enough to anchor properly. 3 mm of side wall in the recess gives the glue real surface to grip, which matters once the magnet is strong enough to try pulling itself out.
✓ Honest N42 grade. We state the grade we actually buy. If you see the same disc advertised as N52 at this size, treat the claim with caution.
What it is
A sintered neodymium (NdFeB) disc, 4 mm across and 3 mm thick, magnetised through its thickness — the poles are the two flat faces, not the curved edge. Two magnets meet face to face, the join sits flat, and the part seats in the same position every time.
This is where the 4 mm range tops out, and the numbers follow the same curve as every other diameter we stock. Going from 4 x 1 mm to 4 x 2 mm more than doubles the pull, 160 g to 340 g. Going from 4 x 2 mm to 4 x 3 mm adds far less, 340 g to 450 g, because holding force follows the contact face more than it follows height.
Worth knowing before you buy: if you can widen the hole to 5 mm, a 5 x 2 mm disc pulls 470 g from a millimetre less depth, and costs less. This size exists for when the bore is fixed at 4 mm and you need everything that footprint will give.
Specifications
| Diameter |
4 mm |
| Thickness |
3 mm |
| Weight per magnet |
0.29 g |
| Material |
Sintered neodymium iron boron (NdFeB) |
| Grade |
N42 |
| Coating |
Nickel-Copper-Nickel (NiCuNi), triple layer |
| Magnetisation |
Axial — poles on the flat faces |
| Pull to steel (calculated) |
450 g / 4.41 N at direct contact, zero gap |
| Magnet-to-magnet pull |
450 g, bare faces in direct contact |
| Shear (sideways) estimate |
Approximately 60 g — sideways load is far weaker than direct pull |
| Drill bit size |
4 mm |
| 3D print hole size |
4.1 mm |
| Maximum working temperature |
Approximately 80°C — standard for N42 |
| Country of manufacture |
China |
Pull figures are calculated reference values for a clean, flat, direct steel contact with no air gap. Paint, primer, glue layers, curved surfaces and any gap at all will reduce holding force, in some cases substantially. Treat these numbers as a way to compare sizes to each other, not as a guaranteed working load.
What you get
▪ The pack size you select from the dropdown: 1, 10, 25, 50 or 100 magnets
▪ Supplied stacked pole-to-pole in a resealable bag
▪ Every magnet is the same 4 x 3 mm N42 disc — the only difference between variants is the count
What this size is for
Well suited to: cast metal gun barrels and weapon arms • heavy resin turrets and sponsons • removable engine decks and hull sections on larger kits • parts mounted on an existing 4 mm pin or post • display plinths and diorama sections that need to come apart and go back together repeatedly.
Choose 4 x 2 mm instead when: 340 g is enough — it needs a millimetre less depth, fits more parts, and costs less per magnet.
Choose 5 x 2 mm instead when: you can widen the hole. 470 g of pull from only 2.2 mm of depth, and cheaper per magnet. Diameter buys holding force far more efficiently than height does.
Working with them
Consider magnet plus steel instead of two magnets. A 3.2 mm recess in both halves of a joint is 6.4 mm of material, which is more than many kit parts can spare. Magnetise one side only and glue a small steel disc or a cut pin into the other. You lose some holding force compared with a magnet pair, but you halve the depth you need to drill.
One magnet lets the part spin. A single disc holds a turret or barrel down but does nothing to stop it rotating. Fit two magnets side by side, or pair one magnet with a locating pin off-centre.
The glue joint is the weak point, not the magnet. 450 g will pull a badly seated magnet out of its hole rather than release the part. Key smooth resin before gluing, wick thin CA down the side walls of a snug 4 mm recess, and let it cure fully before testing.
Slide, do not pull. Separating a stack by pulling straight apart takes the full 450 g. Sliding one magnet sideways off the stack takes a fraction of that and is far less likely to chip the plating.
Keep paint out of the joint. A coat of primer plus two of paint on both mating faces is easily 0.1 mm of gap, and that costs you real holding force. Mask the faces, or fit the magnets after painting.
Honest limitations
▪ You are paying for the last of the diminishing returns. 4 x 2 mm to 4 x 3 mm is 340 g to 450 g — 50% more height for 32% more pull. The right buy when the bore is fixed at 4 mm, the wrong buy when it is not.
▪ It needs real depth. 3.2 mm of recess, and 6.4 mm across both halves of a joint. Many parts cannot give that.
▪ Strong enough to damage the part around it. At 450 g the magnet is usually better anchored than thin resin or hollow styrene. A poorly glued magnet tears out, and a thin socket wall can split.
▪ Sideways load is much weaker than straight pull. Around 60 g. Design the joint so the load pulls the faces apart rather than sliding them.
▪ Neodymium is brittle. These are sintered, ceramic-like magnets. At 450 g they snap together hard enough to chip, crack or nip a fingertip if you let them jump across a gap.
▪ Indoor use. NiCuNi plating resists handling and normal indoor humidity, but it is not a marine or outdoor coating.
▪ Heat weakens them permanently. Above roughly 80°C an N42 magnet loses strength and does not recover on cooling. Keep them away from ovens, curing lamps and hot cars.
Important safety information
Warning — strong magnets. For adult hobby and technical use. Not a toy.
Swallowing two or more magnets can cause serious internal injury. Magnets can attract to each other through the wall of the intestine, causing blockage or perforation. Seek immediate medical attention if a magnet is swallowed or inhaled. Keep away from children and pets at all times.
Keep magnets away from pacemakers, implanted defibrillators and hearing aids. Keep them away from bank cards, hard drives and other magnetic media.
Handle with care — neodymium is brittle and can chip. Store magnets in their bag, away from loose steel and craft blades.
Dispatch
▪ Same-day dispatch on orders placed before 3 PM, Monday to Friday
▪ Sent from our own unit in Derby — we pick and pack everything ourselves
▪ Magnets are shipped within the UK only
Hobby Heaven
By Hobbyists. For Hobbyists.
We are a small family-run business in Derby, run by people who actually paint, build and convert. We publish the grade we buy and the test conditions behind every pull figure, because that is the information we wanted when we were sourcing magnets for our own projects. If something is not right, message us and we will sort it.
N42 Neodymium Disc Magnets — 4 x 3 mm
Nickel-Copper-Nickel coated • Axially magnetised • Packs of 1, 10, 25, 50 and 100
The most holding force available from a 4 mm hole. 450 g of pull for heavy metal parts and jobs where the bore is already fixed.
Why this size
✓ Maximum pull from a 4 mm bore. 450 g — the strongest disc we stock at this diameter. When the hole width is dictated by the part and 4 x 2 mm is not enough, this is the answer.
✓ Calculated pull: 450 g at direct contact. Zero gap, clean flat steel. Magnet-to-magnet also 450 g. Reference value, not a guaranteed working load.
✓ Enough for white metal. Cast metal barrels, weapon arms and heavy resin assemblies stay seated through handling and transport, not just on the shelf.
✓ Deep enough to anchor properly. 3 mm of side wall in the recess gives the glue real surface to grip, which matters once the magnet is strong enough to try pulling itself out.
✓ Honest N42 grade. We state the grade we actually buy. If you see the same disc advertised as N52 at this size, treat the claim with caution.
What it is
A sintered neodymium (NdFeB) disc, 4 mm across and 3 mm thick, magnetised through its thickness — the poles are the two flat faces, not the curved edge. Two magnets meet face to face, the join sits flat, and the part seats in the same position every time.
This is where the 4 mm range tops out, and the numbers follow the same curve as every other diameter we stock. Going from 4 x 1 mm to 4 x 2 mm more than doubles the pull, 160 g to 340 g. Going from 4 x 2 mm to 4 x 3 mm adds far less, 340 g to 450 g, because holding force follows the contact face more than it follows height.
Worth knowing before you buy: if you can widen the hole to 5 mm, a 5 x 2 mm disc pulls 470 g from a millimetre less depth, and costs less. This size exists for when the bore is fixed at 4 mm and you need everything that footprint will give.
Specifications
Diameter
4 mm
Thickness
3 mm
Weight per magnet
0.29 g
Material
Sintered neodymium iron boron (NdFeB)
Grade
N42
Coating
Nickel-Copper-Nickel (NiCuNi), triple layer
Magnetisation
Axial — poles on the flat faces
Pull to steel (calculated)
450 g / 4.41 N at direct contact, zero gap
Magnet-to-magnet pull
450 g, bare faces in direct contact
Shear (sideways) estimate
Approximately 60 g — sideways load is far weaker than direct pull
Drill bit size
4 mm
3D print hole size
4.1 mm
Maximum working temperature
Approximately 80°C — standard for N42
Country of manufacture
China
Pull figures are calculated reference values for a clean, flat, direct steel contact with no air gap. Paint, primer, glue layers, curved surfaces and any gap at all will reduce holding force, in some cases substantially. Treat these numbers as a way to compare sizes to each other, not as a guaranteed working load.
What you get
▪ The pack size you select from the dropdown: 1, 10, 25, 50 or 100 magnets
▪ Supplied stacked pole-to-pole in a resealable bag
▪ Every magnet is the same 4 x 3 mm N42 disc — the only difference between variants is the count
What this size is for
Well suited to: cast metal gun barrels and weapon arms • heavy resin turrets and sponsons • removable engine decks and hull sections on larger kits • parts mounted on an existing 4 mm pin or post • display plinths and diorama sections that need to come apart and go back together repeatedly.
Choose 4 x 2 mm instead when: 340 g is enough — it needs a millimetre less depth, fits more parts, and costs less per magnet.
Choose 5 x 2 mm instead when: you can widen the hole. 470 g of pull from only 2.2 mm of depth, and cheaper per magnet. Diameter buys holding force far more efficiently than height does.
Working with them
Consider magnet plus steel instead of two magnets. A 3.2 mm recess in both halves of a joint is 6.4 mm of material, which is more than many kit parts can spare. Magnetise one side only and glue a small steel disc or a cut pin into the other. You lose some holding force compared with a magnet pair, but you halve the depth you need to drill.
One magnet lets the part spin. A single disc holds a turret or barrel down but does nothing to stop it rotating. Fit two magnets side by side, or pair one magnet with a locating pin off-centre.
The glue joint is the weak point, not the magnet. 450 g will pull a badly seated magnet out of its hole rather than release the part. Key smooth resin before gluing, wick thin CA down the side walls of a snug 4 mm recess, and let it cure fully before testing.
Slide, do not pull. Separating a stack by pulling straight apart takes the full 450 g. Sliding one magnet sideways off the stack takes a fraction of that and is far less likely to chip the plating.
Keep paint out of the joint. A coat of primer plus two of paint on both mating faces is easily 0.1 mm of gap, and that costs you real holding force. Mask the faces, or fit the magnets after painting.
Honest limitations
▪ You are paying for the last of the diminishing returns. 4 x 2 mm to 4 x 3 mm is 340 g to 450 g — 50% more height for 32% more pull. The right buy when the bore is fixed at 4 mm, the wrong buy when it is not.
▪ It needs real depth. 3.2 mm of recess, and 6.4 mm across both halves of a joint. Many parts cannot give that.
▪ Strong enough to damage the part around it. At 450 g the magnet is usually better anchored than thin resin or hollow styrene. A poorly glued magnet tears out, and a thin socket wall can split.
▪ Sideways load is much weaker than straight pull. Around 60 g. Design the joint so the load pulls the faces apart rather than sliding them.
▪ Neodymium is brittle. These are sintered, ceramic-like magnets. At 450 g they snap together hard enough to chip, crack or nip a fingertip if you let them jump across a gap.
▪ Indoor use. NiCuNi plating resists handling and normal indoor humidity, but it is not a marine or outdoor coating.
▪ Heat weakens them permanently. Above roughly 80°C an N42 magnet loses strength and does not recover on cooling. Keep them away from ovens, curing lamps and hot cars.
Important safety information
Warning — strong magnets. For adult hobby and technical use. Not a toy.
Swallowing two or more magnets can cause serious internal injury. Magnets can attract to each other through the wall of the intestine, causing blockage or perforation. Seek immediate medical attention if a magnet is swallowed or inhaled. Keep away from children and pets at all times.
Keep magnets away from pacemakers, implanted defibrillators and hearing aids. Keep them away from bank cards, hard drives and other magnetic media.
Handle with care — neodymium is brittle and can chip. Store magnets in their bag, away from loose steel and craft blades.
Dispatch
▪ Same-day dispatch on orders placed before 3 PM, Monday to Friday
▪ Sent from our own unit in Derby — we pick and pack everything ourselves
▪ Magnets are shipped within the UK only
Hobby Heaven
By Hobbyists. For Hobbyists.
We are a small family-run business in Derby, run by people who actually paint, build and convert. We publish the grade we buy and the test conditions behind every pull figure, because that is the information we wanted when we were sourcing magnets for our own projects. If something is not right, message us and we will sort it.
Specifications
-
Choose Quantity
10
-
Brand
Hobby Heaven
-
Thickness
3mm
-
Type
Disc Magnet
-
Shape
Disc
-
Item Diameter
4mm
-
Grade
N42
-
Coating
Nickel-Copper-Nickel (NiCuNi)
-
Magnetisation
Axial
-
Country of Origin
China
-
Colour
Silver
