The external number range for Equipment master

Dear Experts,

My client has requirement to use KKS code as Equipment number as they want to create Notification and Maintenance order using the KKS code.

For example 10H, 10BEB, 20BHB04, 10LBG10AA001, 10HLA13AA001A, 10ETG10AN001-E  etc.

All these KKS codes has different character length hence it's not fit in any number range.

can anyone suggest the external number range that I can use for above requirement?

Thanks.