These are connecting parts for Plarail Advance, which I created myself after the originals were destroyed by my children. They can be used without problems if you don't twist them forcefully. They have the strength for normal use, but please insert and remove them straight. The shape is designed by a mechanical design engineer, according to the material. I believe the fit is good. Material: ABS This material is used in many LEGO blocks and everyday plastic products. Compared to PLA, which is inexpensive and widely available through 3D printers, ABS contains rubber components in its composition, making it more flexible and resistant to impact and bending. Color: White Set of 28 For those who follow me, and for repeat customers, I'll give you 2 extra! Available from 28 pieces. 28 pieces → 500 yen 35 pieces → 600 yen 42 pieces → 700 yen 49 pieces → 800 yen I will respond if you comment.