Difference in horseman rangefinder cams? 180mm vs 18cm

[crumpet8]

Hi,

Does anyone know if the extra hole makes any difference? Only compatible with certain cameras? The screenshot was too big so here is a link to eBay auctions where the cams in question are visible,

180mm with hole
http://www.ebay.com/itm/Cams-cam-of...226154?hash=item5d698423ea:g:J1sAAOSwmLlX92Zj

18cm without
http://www.ebay.com/itm/Cams-cam-of...948409?hash=item1a1d40fe79:g:OvIAAOSwYIxX92WF