ID markings on 81mm M43A1 fins

[MINENAZ16]

Hello,
What means "THORN" on these fins (original ww2 US HE 81mm M43A1) ?
Is it an US maker ?

 

[HAZORD]

Sebastian, even with my computer set on "Blurr" I can't read it.

Most likely the manufacturer.

 

[MINENAZ16]

A better photo tomorrow

 

[M8owner]

Mine has "SP", so I am going to guess it is the manufacturer.

 

[sgdbdr]

I can't find THORN in MIL-HDBK-1461A "AMMUNITION MANUFACTURERS AND THEIR SYMBOLS" 1998, and MIL-STD-1461E "AMMUNITION MANUFACTURERS AND THEIR SYMBOLS", 1990

 

[MINENAZ16]

A better photo of the marking THORN