2.5 mm x 25 mm Fits M16 castle nut MB165 & MB200 Mini Bikes Always keep a spare Large cotter pin used on the large M16 castle nut on Baja Motorsports Mini Bikes MB165 & MB200 Also used on their 50cc scooters, the Retro RT50 & the Sun City SC50 Large cotter pin used on the large M16 castle nut on Baja Motorsports Mini Bikes MB165 & MB200. Also used on their 50cc scooters, the Retro RT50 & the Sun City SC50. Size is 2.5 mm in diameter and 25 mm in straight pin length (not overall length). A very small part, but one that you absolutely need.,Ask a question about this product: Ask Question Thank you for the question!Questions are usually answered within 1-2 business days.