theNumbers = "1234567890"
objname = "Box5312"
fn filterSufix CorN objName =
(
	sfx = trimLeft (trimRight objName) ; local cnt = sfx.count
	if cnt != 0 do for i = cnt to 1 by -1 do
	(
		if findString CorN sfx[i] == undefined do (sfx = replace sfx i 1 "")
	) ; sfx
)
filterSufix theNumbers objname

Get only object name number as string

Filter sufix number

Maxscript