Hello,
We do not offer any plastic sliders, they are all made of zinc alloy, which makes them very durable.
If your slider does not stay in place, it is either that the chosen reference does not match your closure, or that the product received is defective and in this case a replacement can be made for free.
Do not hesitate to contact customer service, you can send photos of the closure to be repaired for even more precision:
[email protected]
Best regards