Simple spring cotter pin DIN 11024 (flexible cotter pin, locking cotter pin, springlock), locking cotter pin for securing detachable pin connections. Available in 12 sizes in the 1.4 mm - 8 mm range. Available in single, double, and tubular versions, with a galvanized zinc finish and in A2 stainless steel, EN 1.4301, see:
link to product 9261.