This correctly checks if the value is a number but not a decimal.
You are converting the value to an int which cannot have a value past the decimal point unlike the decimal.
So passing ".1" would...

I by no means am an expert in threading but here is what i can gather from this.
you are using 'ThreadPool.QueueUserWorkItem' which queues the item into the current main thread.
What you need to do...

I tried this a while ago, and its not 100% possible because i think not all files contain a header or such that says what the file is

are you trying to create a file that outlook can read? or is this copying the contacts for a different use?