Advice for a "press-fit" THT hole

hello all,

I am in need to specify simple THT plated holes that can retain the component (in this case a solder pin) when I turn the PCB upside down for soldering. I don’t know if the term “press-fit” could be adequate in this context, but anyway it explains very well the objective that I want to achieve. I haven’t found anything useful searching these forums, so here I go.

WAGO 243-131

Based on the above picture and knowing that:

  • the lower part of the pin that is to be inserted in the hole is square
  • the side of that square part of the pin is exactly 0.9 millimeters
  • JLCPCB was a bit vague when I asked the same question; they replied citing their tolerances
  • JLCPCB considers the diameter in the gerber file as “finished”, plating included

Knowing that, in theory, the diagonal of this square should be 1.2728 millimeters and since I have a 1.25 millimeters drill bit, I have made a test hole into a FR4 support and the pin is very very loose and, of course, it falls down.

So what is the correct hole diameter that I must use in the footprint so that the pin will not fall down when I will turn the PCB upside down and, at the same time, it will not be so hard to insert the pin in the hole?

Thank you.

A bit of FreeCAD gets a diameter of 1.208284mm, so I would expect 1.27 to rattle.
As you want the pin to bite into the copper a little, a finished diameter of 1.2mm is about right, maybe even less
A FreeCAD problem
Using 0.21.1, i get 1.27 mm as you would expect from trignometry

I am not surprised you get a vague answer from JLC. Pressfit holes need tighter hole tolerances then the normal production process, and therefore you need t contact your PCB manufacturer and treat it as a custom job. Without explicit communication and agreement with your PCB manufacturer, they may substitute drill diameters for slightly different drill diameters to better fit in their pooling jobs. Insides of holes are often also tinned, and because tin “creeps” this is also not ideal for press-fit.

Except that the corners of your pins are rounded. From what I remember from those pins, they recommend 1.1 or maybe 1.2mm hole. Do you have a datasheet with a recommendation for hole diameter?

But most important is probably the tools you use for mounting the pins. A good DIY method is to buy some tubes (both brass and stainless is available in lot’s of small diameters, stainless steel is for example used en masse for injection needles), and then put a piece of tube into a drill press. Then insert the round end of your pin in the tube and push it with the drill press in the PCB. This ensures you will always push the pin straight in, and therefore you have more alleviation in hole tolerance.

hello David,

thank you for the reply. In theory, your reasoning is correct, but I have made another test making a 1 mm. hole into a bare FR4 support. Of course the pin doesn’t enter, even using pliers. But I have one of the latest PCBs fabricated by JLCPCB that has 1.1 mm. finished plated holes (measured with the caliper) just for this component. Incredible to say, but the pin is loose in almost all holes of this type and it practically always falls down on the bench.

This is why I’m a bit confused. How can a square pin with a 1,2728 mm. diagonal be loose into a 1.1 mm. finished plated hole?

I wouldn’t waste another PCB furniture…

Thank you.

hello Paul,

thanks to you also.

not practicable. I’m building things only as a hobby and I couldn’t afford high prices.

I cannot say for true without a microscope. A magnifying glass is not sufficient. WAGO tells a 1.2 mm. hole; anyway, if you read my reply to David, you can see that I have a previous PCB with 1.1 mm. plated holes (measured with the caliper) and the pin falls down. The friction when inserting the pin is almost always very little. But I also cannot tell if the measure of a so small hole taken with the caliper could be considered affordable.

Only my hands with the aid of a plier. The method that you have mentioned implies to have a press, alas, another not practical solution.


latest reply just arrived from JLC:


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Without an accurate measurement for the corner radius of the pin, it will be almost impossible to determine a suitable hole diameter, and depending on the tolerance of the pins and the holes, you may find that some pins fall out whilst some will not fit at all, which is unsurprising considering that these are not designed to be press fit connectors. A better solution in this case is probably to have a second “backer” board with round holes that will take the round end of the pins, you can then load the main board with holes as specified by the manufacturer and then slip the backer board over the top to hold the pins in place whilst you solder them - this will mean, though that these probably need to be the first part assembled, unless the board is otherwise all SMT on the top side…


I understand. Maybe it’s better that I buy some intermediate drill bits, for example 1.05, 1.1, 1.15 and 1.2 millimeters and try by myself.

JLC told me that if I request, for example, a 1 mm. hole, it will be 1 mm. (+0.13mm/-0.08mm. tolerance) plating included, that’s to say: finished.


I suspected as much :slight_smile:
You write you tried an order with 1mm holes and they were too tight, and with 1.1mm holes and they were too loose. Were those orders from the same PCB manufacturer? But as I wrote earlier, there may be differences in hole size between batches for the PCB pooling services.

You also write you used pliers. That really does not work well. Such pins do need quite a lot of force to insert, so it’s quite possible your 1mm holes were of a proper size.

But if you want to keep price down as a hobbyist, you have no choice but to go with some standard PCB pooling service, and proper holes for press fit is probably too much to ask for. You always have the option to just solder those pins anyway :slight_smile:

hello Paul,

the 1 mm. hole that I tried by myself (not ordered) is too tight. The 1.1 mm. plated holes (ordered to JLC and also measured with the caliper) is a bit loose.

As I wrote to the previous user, I could buy some bits and try by myself. I don’t pretend to use a press to fit the pins in the holes, it’s enough that they have a small friction to retain them in the holes while I’m soldering them. They also have to not move when they are soldered again to attch wires to them.


You could also buy an extra (sacrificial) single socket, place the pin in the socket, place the pin (or force) the pin into the hole, and hold the socket in place with "Blue tac, White tac, or whatever the product is called in your country.
Turn the board over, solder, then remove the “BlueTac” and socket. Move on to next pin placement, repeat as required.

these pins are not part of a socket, their use is to solder wires to them:


Perhaps the solution (time allowing) is to create a test PCB with several holes (5 to 10) at sizes of 1.0mm 1.05mm 1.1mm 1.15mm 1.2mm 1.25mm and get a few PCBs made by JLCPCB. Upon receipt of PCBs test fit your pins and choose the hole that fits as required . . . . then just hope that JLCPCB have a consistent process.


I had also thought to this solution, but about consistency I prefer not to say anything… :slight_smile:

I will think about it anyway.


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If someone is selling pins, they will also sell sockets. Buy a couple and be prepared to throw them away after each has inserted 20 pins.

The purpose of the sockets is to keep the heat from the “Blue tac” so the pins remain in a vertical position while soldering.


this pin is made by WAGO, and you are right, there are terminal blocks that I hadn’t noticed before:


You can’t use press fit pins without a press. These square pins depend on deforming the PCB, and that takes quite a lot of force. Trying to do that with pliers just does not work reliably. So if you don’t want to use a press, then a loose fit and soldering is what is left.

Another idea is to first insert the round sides of the pins into a (sacrificial) PCB. Then put a new PCB on the square pins, turn the whole contraption around and solder the square sides. This helps in keeping the pins straight. But you may have some trouble with getting the “mold” PCB off. It probably has tinned holes and the pins are likely to get hot enough to melt that tin.

ok, but I will try to make some holes with various drill bits before, just to see if I can find one that fits.


That was the idea of using a couple of sacrificial sockets and some “Bluetac” (putty).

It seems the pins are really for wire wrap only so…

what is it?