What size of bit should I use for my horse?

I currently use a 51/2" D-Ring Regular Snaffle and I have the chance to buy a MYLER Full Cheek 5" snaffle bit-- I really want this bit. Myler bits are supposed to be AMAZING and I did my research about them and I want to try it out! Only thing is.there are no distributors in my province of the MYLER brand, so I have to buy off Ebay, and the BEST price for a BRAND NEW Genuine Myler Full-Cheek Snaffle bit..is for a 5" bit. So, is 5" that big of a deal from 51/2"? Should I go ahead and get the 5" bit or keep looking for a 51/2"??

FYI: My horse is a purebred Canadian, 16'1, big boy. (Canadians are light draft type breed if you're not familiar with them)
Answers:
find someone with a 5" bit and measure it in your horse's mouth to see how it fits compared to your 51/2" bit. Unless your horse has a giant mouth you should be ok with a 5". I had friesans here at the barn I work at and the 5" fit with no problem.

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A little bit.

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mickleson

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Aweosme you have a horse well I do too!
But depending on your horses age if he is young I would buy it but if he's older than 8 I wouldn't buy it becasue you have a higher chance of screwing up his mouth.
Hope this helps!

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Put the bit you hvae in his mouth ans look at the edges of it by the d-ring.
Do you have at lest 1/4" on each side of bit or is his mouth filling up the entire 5 1/2" length of the bit.
If you have some sapce a 5" bit would be fine.
5" bits are pretty standard and most horses can use one comfortably. The bit would pinch at the corners of his mouth if it was to small.

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Equipment is never a substitute for good horsemanship.
Did you know many Myler bits are not show legal( I am assuming dressage)

Measure him and compare,,, a well fitting bit is important,, but bit placement is more important,,,Many warm bloods have deep set lips,, if you use the "wrinkle rule" you will find your bumping his teeth,, lower the bit , take of the cavesson, and they learn to pick it up on their own,, and become more responsive.

I start almost 100 young horses a year, have for about 20 years,
That is around 2000 colts,,, I use the same style snaffle on almost everything.. nice relaxed horses who are winning world titles.