Look like BMX style, https://www.google.com/search?sxsrf=ALeKk02SDYOYoPWuYUsB-NaHJ8vO6smhFw:1606423546097&q=how+to+install+bmx+chain+tensioner&sa=X&ved=2ahUKEwiZosuGiqHtAhWMzVkKHYhkDQYQ1QIoAXoECAQQAg&biw=1280&bih=577#kpvalbx=_LhXAX7CYO9SawbkP4_m24Ao8