40mm Miniature dc Motor, RE Model. Motors intended to be used with planetary gearheads; assembly of the two is quick and easy, requiring no special tools Motors can be used with GP42 42mm gearheads e.g. (stock no. ; 420-5041 420-5041 ) using fitting kit (stock no. ; 468-4775 468-4775 ) Speed Constant: 581rpm/V (stock no. ; 468-4797 468-4797 ); 317rpm/V (stock no. ; 468-4804 468-4804 )