Our general rule is that Babe Ruth is the key card to any set in which he appears, but due to the extreme rarity of the Casey Stengel (just one example is known), such is not the case with the Maple Crispette issue of 1923.  Still, Ruth would be the second key, clearly the most valuable card from the issue that is actually attainable.  Issued by a Canadian candy company, the Maple Crispette cards were redeemable for baseball equipment, which is what has led to their scarcity today.  This example has been graded GOOD 2 by SGC, a well-worn specimen that nonetheless boasts strong eye appeal for the grade.  An extremely difficult card of Ruth, one of just 52 examples graded by PSA and SGC combined - which, for a Babe Ruth card, is quite an illustration of the card's relative scarcity.