Sexing sailfin plecos ... help please!

[Scottishgirl]

I'm new to this site so please forgive I post this incorrectly. I did have a good browse through other questions and anwers but couldn't see any info concering my queerie.

I understand from the info on this (rather excellent! ) site that you can sex sailfins by their "stumps". Please tell me what a stump is!!

Apparently the male has a small set thick stump and the female's stump is reversed and lies flat.

Could some lovely kind soul please put this info into very very basic terms please ... I'm sure it's quite obvious but at the moment I'm struggling to understand

Thank you very much