When building should be careful to remove the cap from the shock, otherwise you can throw away the barstool. But that will never be seen and so that you may destroy the product is a no go. The cap would have to be a bit thicker, so that they can not be plugged only into the stump. Now I can throw away at least one of the two stool :(.
For those who have already done the mischief and the cap is now stuck in the stump:
1) cut out with a knife to the lower part (inside the cone), which goes quite easy because the diameter is larger than the plastic and it can easily be cut.
2) The plastic that has set itself the thread is significantly more persistent. Here actually only helps it anzuzuenden with NEM lighter and place in sink ... NEN window open and do not forget to wait until the plastic has been dissolved ...
3) Should work again :) (quick & dirty)