For your Rockwood Ultralite RV roller shades measuring 23 inches in vinyl length with a 3/4 inch core and a 15-inch spring, you will likely need the small replacement spring designed for this size. Elkhart RV Parts offers the Irvine replacement spring 3/4" version for value-line RV roller shades, which is commonly used in such applications. The black and clear dials on your shade are likely part of the tension adjustment mechanism but do not affect the spring type needed. Between the slow-rise and value-line springs, most RV manufacturers choose the value-line spring as a cost-effective option. To confirm the exact spring size and type, use Elkhart RV Parts’ Quick Spring Finder tool available on their website. This tool helps you select the correct spring based on your measurements and shade details. You can then order the replacement spring directly from their site to restore your roller shades’ locking function.