You can shoot spares with or without your thumb the only thing is if you don't use your thumb is that the ball can't have a weight hole and a thumb hole.

Some of the things I have heard is if you use two hands, then you must always use two hands even if just shooting 10 or 7 pin.

Then earlier this week I was watching a kids league and one of the young men was a two handed bowler. He eventually became frustrated with the way he was scoring and started to use one hand (same dominant hand) on his first delivery. I was told that it was not illegal because it was a scratch league but he couldn't do that in a handicap league.

With the update to the drilling of balls for no thumb bowlers, you would not be able to use the same ball for two hands and one handed.  The new rules for drilling on no thumb balls changes the grip center to the fingers and not the center of the palm. IF the ball was drilled for two handed delivery, no thumb, it would more than likely not meet the static weights to be legal for a one hand delivery with the thumb being used.

if a ball is scaled out for a NO thumber it can still be legal for a bowler that uses his thumb ( I know this for a fact  because I have scaled every balll since the new rule was made and its legal both ways you put it on the scale) . I have been drilling up equipment for over 25 years and all of my ball have had a thumb hole in them so it would still fit my hand if I ever wanted to throw the ball with my thumb in it if I decided too. ON the new rule it does help a lot if your to have equipment with no more then 2.5oz of top weight if your wanting to go pin up on your drilling layout.  I had a few balls that had a weight hole in them and all I had to do to fix the side weight was to plug the hole and drill the ring finger deeper to make it legal under the new rule of the center of my fingers instead of the middle of my span.  Trust me   a NO thumber has less options now on how there able to drill up there equipment do to the new rule on gripping holes. But 1 things for sure there are still ways around this rule to make balls legal with out a weight hole, How do I know this  I have found at least 3 different ways to do it so far and IM sure ill find more with more time. the rule states you cant have a weight hole but it allows you to have a pinky hole as a weight hole if your pinky can fit in that hole   as long as IM able to put my 1st finger in 1 hole and my middle finger in the 2nd hole I can have my pinky fit in a normal weight hole as long as its with in stretching your hand out and the hole can be any size you'd like as long as your able to show your able to put fingers in all the holes and it does not say you have to throw it that way though   just deminstrate your able to get your fingers in the holes is all. like I said from day 1 on this new rule, there are still ways around it and always will be. USBS should of just pulled up there big boy pants and said  the CG had to be with in 1" of your center of grip  with NO weight hole what so ever and then everyones is on the same playing feild but they didnt and they totally missed it on this new rule. Its all good still because IM still able to put my CG more than 1" way from my center of finger  holes and I can still make the ball legal with a pinky hole as my weight hole, so what did USBC thought they had it all figured out when they really didnt.    I call that a swing and a miss  LMAO

I can't see USBC making the 1: CG rule because it will effect more bowlers that use there thumbs an thats not the USBC is trying to fix LOL  they made a atempt to clarify the rule better and that back fired on them if you ask me..  if USBC made this rule that the CG had to be with in 1" of the CG line there would be way to many balls out there that would have to be fixed and the cost would be outragest and I just dont see that happening.  IF the USBC is more worried about 2 handers and no thumb bowlers when there are bigger concers i think they really need to focus on like how do you change a nother rule on awards almost at the end of a season  which was 3 months prior to aug 1st.. if you threw a 800 set or a 300 game in the 2014 season then that would be the last 1 youll ever get unless you pay for them from here on out. How messed up is this? VERY!!!!  I guess if there not going to be giving out rings that means the cost of USBC memberships should lower yes? I highly doubt that either. they will save tons of money on awards alone and do you think as USBC members it will bennifit us the bowlers in any way?  I cant see that it will.. just another rule USBC messed up with and how they went about it.. It will be good to get someone new in there next season thats for sure...  Just a nother point on how the USBC  tryes to always change things mid stream and put a kink in things..