Piezo handpieces are not all created equal. In fact, they fall into two distinct categories: the EMS type and the Satelec type. The important difference is the thread pitch which is finer on the EMS and courser on the Satelec. The only difference that you can see is the Satelec style has 2 flats where the tip wrench goes, and the EMS has 4 flats.
If you (or your customer) purchase the wrong tips by mistake, they will only go on about half way (see picture to right). If you use the tip wrench you can force it on, and it will go but stripping the threads is the outcome. Soon you will have the results you see in the bottom picture. The threads stripped or broken off entirely (picture bottom right).
The replacement tips cost between $65 and $100, and the handpieces cost between $250 and $500. Say an office has one EMS scaler and 5 tips that they use on a regular basis. Now, one tip breaks, so the office manager orders a new one from the picture in the catalog and gets the Satelec by mistake. The Dr. starts to use it, and it won't go on, so he uses the wrench and forces it to fit. He has now distorted the threads. The next time he puts on the right tip on but it is tight too. So he forces it on, and it works okay. Over time, he will destroy the handpiece and all the tips costing around $1000.
So, What to do?
Know what you have and purchase only the proper replacement tips.
If you are using a new tip (or any tip) ,and it will not thread all the way down easily with just your fingers, STOP and do not force it.
If a Dr. sends you a scaler handpiece, and the threads are stripped or broken off, they need a new handpiece.
If you are selling tips or handpieces to your customer, make sure you check all these things. You don't want to be the cause of the problem.
If you are going to send us a handpiece for repair, please be aware that very little can be done to save them. I can fix water leaks, clean electrical contacts, and replace broken plastic parts, but not much more.