# The third system: why I built push-fit, and what it does that a thread cannot
July 2026 · Body Art News · Poli International
Disclosure before anything else. I created the push-fit system, in the early 2000s, for BioFlex®. I am the creator of BioFlex® body jewelry and I sell it. Everything below is my own engineering reasoning and what I saw across years of piercing people and following them afterwards. Read it with that in mind, and judge the mechanics rather than the messenger.
We have already compared internally threaded against threadless, which is the choice most people are offered. But that comparison is incomplete, and I am partly responsible for the confusion, because the third system is mine and its name was taken.
» There are three connecting mechanisms, not two. A machined thread. A bent pin held by tension. And a tapered interference fit, which is push-fit.
» The names collided. Much of the industry, including NeoMetal's own material, uses "push-fit" and "press-fit" as loose synonyms for threadless [2]. They are not the same mechanism.
» Push-fit was designed as a safety feature first. The motto I gave it was: lose a jewel, not your skin.
» The market adopted its dimensions. I set the internal hole sizes as a standard, and metal push-fit attachments followed in steel, titanium and gold.
What each system actually is
The thread
This is not jewellery manufacturing. It is precision engineering. The threads are metric and very small. Most internally threaded jewellery uses a 0.8 mm thread, 2 mm long, and the main alternative is 0.9 mm by 2 mm in metal. Those two are not interchangeable, and that single tenth of a millimetre is the practical reason an end from one maker may not fit another maker's post. Cutting them demands micro-precision and tooling that costs a great deal on top of the material, which is why the piece costs what it costs. Anatometal, who make it well, describe the difficulty exactly: it requires "precise machining to ensure a threaded hole is placed within the barbell end without compromising its durability, regardless of the gauge" [4].
Its real virtue is certainty. Once the piece is seated, the wearer is unlikely to lose the attachment.
The bent pin
NeoMetal invented threadless in 1997 and makes it in implant certified titanium to ASTM F-136 [2]. There is no thread at all. Retention comes from tension: the pin is inserted about a third of the way into the shaft and bent between 10 and 20 degrees, and a greater bend gives a tighter fit [3].
I want to be fair about this, because it is a real advantage and I do not have it: retention you can tune is genuinely useful. A wearer who changes ends often can have them set loose, and someone who never does can have them set firm. That is a proper design benefit, not a marketing one.
The tapered fit
Push-fit looks like a threaded piece from the outside, which is deliberate. Inside, there is no thread anywhere. The labret base has a tapered hole. The attachment has a tapered post, slightly over the size of that hole. It goes in easily because both parts are tapered, and then it holds by pressure across the whole contact surface.
No thread to cut, no pin to bend, no setting for anyone to get wrong.
Why I built it
I was not trying to compete with anyone and I was not trying to make something cheaper. I kept seeing the same injury: a metal piercing caught on something, and because the jewellery would not let go, the tissue did.
That is a design decision, even when nobody has consciously made it. A threaded connection has no release. If a baby kicks the navel bar its mother is wearing, or a jumper catches a nipple ring, the strongest part of that assembly is the joint, so the weakest part is the person. The client keeps the attachment and can lose the piercing, sometimes with an open cut that needs stitching.
Engineering solves this everywhere else with a deliberate weak point: a shear pin, a breakaway coupling, a ski binding that releases before the leg does. That is all push-fit is. The joint is set to hold through everything ordinary and to let go before your skin does. Better to lose a jewel than to go to hospital.
This is the part I would most like people to take away, because it reframes the whole comparison. A threaded piece is not more *secure* in a way that is purely good. It is unreleasing, and that is a different property with a different cost.
Cleanability, which nobody discusses
The second reason is hygiene, and here I am giving you my judgement as a manufacturer and a piercer rather than a published study.
When you insert a threaded labret, the cavity collects body fluid. Once the attachment is screwed on there is no practical way to clean inside it, and it can stay that way for a long time. A thread is also, geometrically, a spiral trench: it is the hardest shape to clean and the easiest to hide something in.
Threadless has a different version of the problem. The pin is thin relative to the hole it sits in, and because you cannot generate high tension on a thin-gauge post, a gap remains. Anything that moves the attachment works that gap.
A tapered interference fit has neither. The surfaces meet along their whole length, so there is no void to fill. And with no thread inside or outside, every component cleans and sterilises easily, because there is nothing to clean around.
What it gives up
One real drawback, and it is not a small one for some people: the visible part is polymer. Not everyone wants to wear plastic on the outside, unless hiding the piercing is exactly the point.
That is the honest trade. I made a safety and hygiene decision and paid for it in materials.
The part nobody has written down
When BioFlex® launched I designed the internal hole sizes to be a standard, on purpose, so the system would not be a closed garden. Other manufacturers began making attachments to those dimensions, a post about 3 mm long and 0.8 mm in diameter, tapered, and metal push-fit attachments appeared in steel, titanium and gold. An invention made for polymer ended up setting the dimensions for a metal product category.
There is a stranger consequence that I have never seen documented anywhere. The vast majority of threaded attachments will screw straight into a BioFlex® internal labret. So someone who prefers threaded ends can use them in a push-fit labret, and they get something better than they had: an external thread on the attachment cleans far more easily than an internal thread down a cavity.
What they give up, and they should know it, is the release. Screw an end in and the fuse is gone.
The systems have been quietly interoperating in people's faces for twenty years and nobody wrote it down.
Where it sits relative to the standard
The Association of Professional Piercers publishes what much of the industry treats as the reference for initial piercing jewellery, and it lists internally threaded and threadless [1]. Push-fit in the sense described here is not in it, and neither is any polymer system.
That is worth knowing rather than arguing about. The standard grew up around metal, and it describes the metal systems thoroughly and well. What it is not is a complete map of the field, so if you are weighing materials as well as mechanisms, it is a starting point rather than the last word.
FAQ
Is push-fit the same as press-fit or threadless?
No, and this is the most common confusion. Threadless holds by the tension of a bent pin [3]. Push-fit holds by a tapered interference fit with no pin and no bend. The industry uses the words interchangeably, which is why the distinction keeps disappearing.
Will it fall out?
It is set to hold through ordinary wear and to release under a real snag. That is the design, not a defect. If you want a connection that never releases under any load, you want a thread, and you should understand what that means for the tissue.
Can I use my existing threaded ends?
Usually, yes: most threaded attachments will thread into a BioFlex® internal labret. You gain easier cleaning and you lose the safety release.
Is this only for healing piercings?
No. BioFlex® is certified to ISO 10993-6 and the resin holds USP Class VI biocompatibility, so there is no biological limit on how long it can be worn. The idea that polymer is a temporary phase came from rules written around a different class of material.
Patrick's note
I made push-fit because I thought I had to do something, not because there was money in it and not out of any competitive spirit. I am not against threaded and I am not against threadless. Both are made properly by people who care about it, and both do things mine does not.
What I would ask is only that the third system gets counted. When the choice is presented as thread or bent pin, a whole approach to the problem goes missing, and with it the question I think matters most: when this joint finally meets a force it cannot hold, what do you want to fail first?
I decided a long time ago that the answer should be the jewellery.
