I have had difficulty finding an answer online, but maybe someone here can help. I have been shooting Nockturnal - S lighted nocks and wanted to buy a few more. The local shop was out, so I ordered some online. What I received was the size S also (according to the packaging) but the part # was different NT-203. The original packaging I have been shooting were NT-205. The new ones are a larger diameter and do not fit into my arrow shaft. I can't find an answer online if the S changed at some point. I stopped in Bass Pro this week. They had the S in stock with the NT-205, but not having the original with me I didn't feel like buying on the hope that it's the same, at least until I can find an answer. The guy working the archery section didn't know and said the S should only be one size and was unaware of any size change, which was the the same basic response I received while in another bow shop. I can't find any part #s on the Nockturnal website either.