York Locomotive Works offers custom, LEGO® compatible train parts. intended to fit and function as LEGO elements. However because of tolerance variances in the 3D printing process, I cannot make any guarantee regarding the fit and finish of any individual piece. Every effort has been made in the design stage to make sure parts are sized correctly, but variations in the 3d printed result will occur. As a result, you may receive a part that will not fit as well as it could. I have however had a decent success rate with test models fitting and functioning well and hope you have the same experience.
York Locomotive Works is not afiliated with or endorsed by the LEGO® group.