We took our signature 1-selling shingle, Timberline HD and transformed it by strengthening the common bond and creating the industry's largest nailing zone. Timberline HDZ Shingles have the same renowned Timberline quality and performance you know and love, with improved nailing accuracy and installation efficiency. Timberline HDZ Shingles are easy and fast to install, with an incredible 99.9 percentage nail placement accuracy. Results based on study conducted by Home Innovation Research Labs, an independent research lab, comparing installation of Timberline HD Shingles to Timberline HDZ Shingles on a 16-square roof deck using standard 4-nail nailing pattern under controlled laboratory conditions. Actual results may vary.