Crankcase drain plug - lenght?

Hello,
Can you tell me what should be exactly lenght of crankcase drain plug (part number 453-11)? I'm not sure mine because I can screw about 2/3 of the plug lenght and than is hard. I do not want to destroy crankcase so this is why I'm asking.

as far as i know, the thread is conical
therefor you can screw it for 2/3 of it's lenght and than it's closing up and sealing the thread and hole
without sealant.
JP