Hi SHW60,
The Fischer SX Nylon Plugs 6 x 30mm 100 Pack (Product Code 98684) can be used with 4mm screws. However, it is important to select the correct length as Fischer say that with this plug the screw must protrude from the end by around 5mm for it to work properly, so plug length would be screw length plus fixture thickness minus 5mm. It may be worth asking Fischer about this at technical@fischer.co.uk
Thanks for using Screwfix Q&A. JT
Answered by: JTremain
Date published: 2019-10-29