This is a replacement fin can for the Estes Falcon 9 flying model rocket.Print at a 45 degree angle or the attachment tabs will not have enough strength.
https://estesrockets.com/products/spacex-falcon-9?srsltid=AfmBOoo2jXq4sJlNBamOgu8brjlp8HugRL9mbWRW9LbQUCUNmhK70qcj