Picked up a 2pc header set with midpipe. Consists of 2x 2-1 in to a 2-1 mid pipe. The tubing diameter is substantially larger than stock. I cannot find a listing for this kit anywhere or even find a picture of a kit that looks like it. I bought it off marketplace from a shop that was closing and it had all the tags on it with 1999-2000 cbr 600f4 labels on the tags and written on the pipes as well. Everything lines up beautifully however, with the diameter of the tubing being larger the heads of the studs on two of the pipes touch the tubing not allowing a socket on them without altering the direction the studs going ultimately starting a cross thread or stripping the threads in the block. Are there studs with narrower heads that I just can’t seem to find? The inside diameter of the new gaskets is 41mm….. considerably different from the stock 35mm…..
all put together the kit is perfect! The bends are in the right spots and it looks phenomenal with the 2 piece header ceramic coated and the midpipe stainless! The SC projects slip on looks dynamite attached right to the midpipe exhausting right behind the foot peg.
if it wasn’t for the stud issue, it would be on. Any advice or anyone know what studs to use? Will post pics of headers hoping someone recognizes them and can let me know what brand or any info on them.
just got setup on here and wish I did a long time ago! Look forward to any info anyone has! CHEERS!

 

Welcome to the forum, you could try some brass 8mm (i think) nuts with no flange that might do it... or unfortunately the wrong headers.
I have never come across any that are significantly larger, could it be from an RR?