The revived instrument had changed in specific ways. In the mid-18th century, the bell flare increased, crooks fell out of use, and flat, removable stays were replaced by tubular braces. The new shape produced a stronger sound, suitable to open-air performance in the marching bands where trombones became popular again in the 19th century. Before the early 19th century, most trombones adjusted tuning with a crook on the joint between the bell and slide or, more rarely, between the mouthpiece and the slide, rather than the modern tuning slide on the bell curve, whose cylindrical sections prevent the instrument from flaring smoothly through this section. Older trombones also generally don't have water keys, stockings, a leadpipe, or a slide lock, but as these parts are not critical to sound, replicas may include them. Bore size remained variable, as it still is today.