Need some Regex Help

I need help generating a Regex to test the following (I admit I am no good at this):
Up to 5 digits, and an optional 6th Alpha Only character.  So the pattern would be:

I started with /^\d{1,5}[a-zA-Z]?/ but this allows a letter in the middle, not just as the 6th character.
This will be tested using the System.Text.RegularExpressions.Regex .IsMatch method in a C# class as the characters are being typed (think a specialized input mask).

Thanks for any help!
ericlockshineDirector of ITAsked:
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Dan CraciunIT ConsultantCommented:
You need an alternation:

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ericlockshineDirector of ITAuthor Commented:
Works like a champ!
Dan CraciunIT ConsultantCommented:
Glad I could help.
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Regular Expressions

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