14mm female to 18mm male glass adapter. If Amazon doesn’t have it, most smoke shops should.

https://www.amazon.com/dp/B07LGX32WT/ref=cm_sw_r_cp_api_i_tVrHEbQHQFYAE

I'd suggest this instead of the glass slide. If you arent on a budget I'd buy two packs. One of the 4 should perfectly fit your vapcap without it falling through the adapter.

https://www.amazon.com/gp/product/B07LGX32WT/ref=ppx_yo_dt_b_asin_title_o04_s00?ie=UTF8&psc=1