This is a bag of 40x Plastfast30 3.5 x 16mm screws.
These screws have a special thread profile and are designed for screwing directly into holes in plastic. They secure extremely well due to their large thread engagement, yet are much less prone to splitting the plastic. Ideal for screwing into printed pilot holes.
Great for use in projects that would otherwise use trapped nuts or threaded inserts, these screws are a quick, easy and cheap way of holding together printed parts securely.