My 1.875" Novak holder uses 8-32 x 5/8" long screws (length of threaded section, not total length of screw). As best I can measure on your photo, the screws are exactly the same as mine. Novak was big on commonality between products, so its no surprise they would be the same. You can go long on the screws and it wont hurt anything -- they just thread up into the diagonal holder. 3/4" long is a more standard size.
Probably a bag of 5 screws at Home Depot will be under $1. You could pick up some 10-24 x 3/4" long and 10-32 x 3/4" long for extra insurance, but I'm 99% sure they will be 8-32.
Although I notice your holder looks modified, so maybe going long is a bad idea. Might hit the glass on the right side of holder in the photo. Maybe take a file with you in case you get into trouble on the length.
It looks like one of the screws is right up against a spider vane. So knobs is probably not going to work. Hex socket head (Allen wrench) will probably be fine.
Edited by ngc7319_20, 24 June 2019 - 01:50 AM.