Yes that is because you were looking at larger chucks that have to hold a lot of weight against rotational and cutting forces. Here is a link you will see what I mean at the bottom when you get to the smaller chucks. I can not tell you what they style exactly. that all depends on the tolerances of the machined elements.

These are a type of lathe jaw for a chuck. There are thousands of kinds. most have 2 retaining screws but because these are so small they will never carry such a heavy load that 2 screws would be necessary. They likely fit a 2 or 3 inch chuck or the metric equivalent.

References:

https://www.google.com/search?q=chuck+jaws&source=lnms&tbm=isch&sa=X&ved=0ahU...

Reason:
I couldn't find any that look like these or use only one screw. If you could narrow it down with a more specific link, that would be really helpful. Thanks.

Yes that is because you were looking at larger chucks that have to hold a lot of weight against rotational and cutting forces. Here is a link you will see what I mean at the bottom when you get to the smaller chucks. I can not tell you what they style exactly. that all depends on the tolerances of the machined elements.

References:

http://www.pml-pal.com/products/turning-chuck/