This is a small parts choking hazart tester. This specially desiged cylinder is used to test if small items may be a choking hazard for children under 3.
In the U.S. there are regulations on small toys and other items that are intended to be used by children under three. This regulation prevents deaths and injuries to children under three from choking on, inhaling, or swallowing small objects they may “mouth”. It bans toys and other articles that are intended for use by children under three and that are or have small parts, or that produce small parts when broken. The test for "small parts" is found 16 CRF 1501.4: in https://www.law.cornell.edu/cfr/text/16/1501.4
This is a 3d model of the part described in the regulations.