O2 sensor bung/blank

I recently bought a Spark decat pipe, it didn't come with the bolts to blank off the O2 sensor holes. Can anyone point me in the right direction? I don't know what size they are.

Also the one near the front is the same size as on the original cat but there is another one near the back that is bigger, I have no idea what this is for as my bike only has one Lambda sensor. (Maybe the S2R 1000 has two?)