They are available in several lengths sizes(specially designed radius on top and bottom of joints) as desired by customers. these are specially double rolled Alloy steels Bar.
They are available in 2 7/8",3 1/2",4 1/2", 5 1/2" sizes For any hole combinations

Source :- https://www.sledgehammerasia.com/accessories/joint-key.html

Sledgehammer Oil Tools Pvt. Ltd

SledgeHammer is one of the leading centralizer manufacturers and API & ISO certified 14001, 18001 and, 9001 certified company known for its quality cementing products. Presently, it enjoys the reputation for being the largest manufacturer of cementing products and suppliers of offshore and onshore cementing and float apparatus in the entire Asia. This makes it the only source for quality and original equipment.SledgeHammer is a pioneer in production and designing of innovative cementing products.SledgeHammer is a manufacturer of Quality Cementing Tool, Bow Spring Centralizer, Solid Rigid Centralizers, Cement Basket, Cementing Plug, Cementing Head, Stop Collars, Float Equipments, Stage Cementing Tool, Bridge/Cement Retainer, Dopes & Compounds.