This　paper　is　a　study　on　the　mechanical　behavior　of　grade　8.8　and　10.9　small-sized　(M14-M20)　bolts　with　the　thread　into　the　bolt　hole.　A　total　of　eighty　specimens　with　different　thread　depth,　surface　treatment,　bolt　diameter,　and　bolt　strength　grade　were　subjected　to　static　loading　tests.　The　effects　of　different　parameters　on　the　properties　of　specimens　such　as　ultimate　bearing　capacity,　initial　slip　load,　ductility,　and　initial　stiffness　were　systematically　investigated.　It　was　demonstrated　that　the　typical　failure　mode　is　bolt　shear　failure.　The　increase　in　thread　depth　causes　the　ultimate　bearing　capacity　of　bolted　connections　to　decrease,　and　other　design　parameters　also　have　effects　on　the　ultimate　bearing　capacity.　The　ultimate　bearing　capacity　of　bolted　connections　with　shot-blasted　surfaces　is　greater　than　that　of　bolted　connections　with　wire-brushed　surfaces.　Moreover,　bolted　connections　with　a　greater　thread　depth　have　a　lower　yield　strength.　The　method　of　contact　surface　treatment,　bolt　diameter,　and　strength　grade　also　affect　the　yield　load　of　bolted　connections.　The　initial　stiffness　does　not　change　much　with　the　increase　of　the　thread　depth.　In　addition,　the　increase　in　thread　depth　decreases　the　ductility　coefficient　and　ultimate　displacement,　which　has　a　negative　effect　on　deformation　performance,　and　the　ductility　coefficient　of　bolted　connections　also　decreases　with　the　increase　in　bolt　grade.　Finally,　based　on　the　test　results,　a　design　formula　for　predicting　the　ultimate　bearing　capacity　was　proposed,　and　the　calculation　results　match　the　experimental　results　well.　The　difference　in　ultimate　bearing　capacity　due　to　thread　depth　can　be　well　described　by　the　formula.