All About Pocket Knives

I have a Queen Trapper that I need help with pattern id , I need to order a replacement main blade.
Do I measure the closed length ? The main blade has been used/sharpened to almost nothing.
Using fb groups I've been told three different patterns for this knife .. #19 , #33 and slim line so I need help.

I forgot to mention this dates 1973/1975

Pattern is a "Trapper" as you say, but measure closed length to see if it is a Trapper or Mini-Trapper. It needs a new Clip blade. I do not know Queen pattern numbers but stating closed length will get you the correct blade.
Queen is no longer in business but i'm sure there are 'dealers' with Queen blades & parts.
kj

The closed length is 4" ... and yes , I've found what appears to be a wealth of different blade and parts that were bought at auction when Queen closed up shop. .... BTW thank you Sir.

This might help: https://queencutleryhistory.com/

Howdy Pepaw, to AAPK!
You have what we call a HOK here on AAPK. HOK is short for honest old knife.
I would venture that your knife is a pattern #24 since it's 4" closed. I can't quite make out the tang stamp in the picture but it appears the "Q" is upside down, maybe.
On one list your is called a Slim Trapper and the Queen catalog #50 ('72-'78) it is referred to as a Stag Trapper.
There are at least three 4" Slim trappers listed, the #24, #11 and #30.
Just looking at your knife, it appears to have many more miles in that clip blade.
Treefarmer

Your knife is a #19 trapper and it probably measures 4 1/8".
The slim trapper is a close measurement at 4".
The obvious difference in a standard vs slim is the center pin placement.
The slim trapper's pin is more offset and closer to the end cap.