Rule No. 20 at Part III of the Laser-Class-rules describe the allowed diameter of an Inspection-port. The rules you can get for example at www.laserinternational.org .
Don´t forget to visit drLaser-website (link is here at TLF-forums-index-site) there at "FAQ" and "maintance&fittness", you will find something about Inspectionports and fixing the maststep (if needed). DrLaser website-also can link you to the rules.