Why does eos block hash id not include character like "ghijklmnopqistuvwxyz"?

Question

I fetched all the hashid of blocks from mainnet (block num 92077797~92150300) I noticed that the block id have no any characters like "ghijklmnopqistuvwxyz"

Here is the test result with command for i in {a..z};do echo $i;echo "scale=4;$(cat hashfile |grep "$i\""|wc -l) / 72838"|bc;done

a
.0631
b
.0636
c
.0633
d
.0621
e
.0614
f
.0626
g
0
h
0
...
x
0
y
0
z
0

Answer 1

That would be because the hash is in HEX representation and not WIF or any other encoding. Hex is short for hexadecimal and comprises of the 10 digits 0-9 and the letters a-f