How wide do I have to stretch my anus in order to comfortably and successfully open an XO sakurai speculum or an anal expander for a while without pain?

[Carlwheezr]

Everytime I try to use a speculum on myself to open up my hole wide I feel discomfort and pain. Anyone know how wide or loose I have to be in order to use a speculum or anal expander to keep it open for a while and not be in pain? 

Edited December 4 by Carlwheezr
forgot tags

[Fistedmike]

At the time I had my Sakurai XO speculum, I was fisting most everyday. Punch fisting was always part of it, so my hole would open readily to take a fist or large toys. I could open the speculum up to about 4” without any discomfort. I am small framed, so I think my restrictions would be due to my bone structure. Now that I don’t have the freedom to fist as frequently as I did back then, it would be a challenge just to get it in. I suppose what I’m saying is that it takes almost daily stretching to be able to take anything that large without discomfort.