I'm wondering this too. I know the 6" DP Deluxe stalk is too short for Mystery helmets. Thanks to Handshaub, I have a 7" aluminum stalk on my Mystery (from earpiece top to rangefinder bottom) and it looks right to me. Anyone making 7 inchers??
I've almost completed building an aluminium RF stalk (hollow) from scratch, after much deliberation and photo comparrisons I decided on a 7" Stalk, seems right.