Tube mounting holes - FPIII

[Laudanum]

Warning, there is a dumb question in this post, like most of my questions are  :-) 

 I am wondering why the tube socket holes are actually larger than octal socket holes generally are? 

And related to that, and this is the dumb part ... is there any reason why the included O-ring has to be used to mount the octal socket if an alternative can be found? 
I am installing octals in my build in place of the 9 pins to use 6SN7 tubes and with the tube holes being a bit larger than standard octal cut-outs, I found an alternative way to mount the octal sockets rather than using largish silicone O-rings.  I have small O-rings on hand that actually wedge in between the tube socket and the mounting hole thus perfectly centering the octal tube sockets.  In my opinion, it looks better and simplifies mounting but I wanted to make sure that there isnt anything that I am missing that necessitates the use of the larger silicone o-ring/rings included with the kit?

Thanks

[Doc B.]

At the time that PJ and I worked on the FPIII, the mid 2000s S.E.X. kit and the original Paramount we thought to try offering a sort of universal mounting hole based upon the notion that there are some alternate tubes one could try that require sockets that are a larger diameter. That is why the hole is a little big for the octal socket that we supply. You can mount the socket any way you wish, I simply chose a silicone o-ring that would stand up to the heat and as a bonus offer some damping to help reduce the transfer of chassis vibration that could contribute to microphonic behavior from the tube.

We are moving away from this concept because the required adapters add some expense to the kits and we don't hear of more than a few hardcore users taking advantage of the "re-scalable hole".

[Laudanum]

Thanks for the explanation, Doc.  Makes sense now.

Thanks