This is for Ethereum wallet, not bitcoin
An example private key
In Bitcoin, a private key is a 256-bit number, which can be represented one of several ways. Here is a private key in hexadecimal - 256 bits in hexadecimal is 32 bytes, or 64 characters in the range 0-9 or A-F.
E9873D79C6D87DC0FB6A5778633389F4453213303DA61F20BD67FC233AA33262