Okay Tuma now I finally see on the vid what you ment by the clip to the mainsheet.

It's a Wichard click-clip with 10mm hole; according to the manufacturer it can stand a load of 7000 newton ! For me it's sufficient

RAIDER-15 (homebuilt)

hey boy, what did you do over there, alone far out at sea?..
"huh....., that's the only place where I'm happy, sir.