diff --git a/release.md b/release.md
index eac680c7..b3644aed 100644
--- a/release.md
+++ b/release.md
@@ -21,6 +21,7 @@ Full docs @ https://docs.grid.space/projects/kiri-moto
 * add CAM Z bottom visualization, make it relative to stock instead of part
 * add CAM Z bottom inversion option to flip operator
 * add CAM custom gcode operator (can be used for pausing, too)
+* add CAM z extend option on registration op independent of "Z Thru" global
 * add optional CAM operation notes (helps with many similar ops)
 * add option to limit CAM trace ops to Z bottom limit (when in use)
 * extend url loading of workspaces to all formats
diff --git a/src/kiri-mode/cam/client.js b/src/kiri-mode/cam/client.js
index 542205d9..47d03d4e 100644
--- a/src/kiri-mode/cam/client.js
+++ b/src/kiri-mode/cam/client.js
@@ -1153,6 +1153,7 @@ CAM.init = function(kiri, api) {
         dwell:   'camDrillDwell',
         lift:    'camDrillLift',
         feed:    'camRegisterSpeed',
+        thru:    'camRegisterThru'
     }).inputs = {
         tool:     UC.newSelect(LANG.cc_tool, {}, "tools"),
         axis:     UC.newSelect(LANG.cd_axis, {}, "regaxis"),
@@ -1163,7 +1164,9 @@ CAM.init = function(kiri, api) {
         down:     UC.newInput(LANG.cc_sdwn_s, {title:LANG.cc_sdwn_l, convert:UC.toFloat, units:true}),
         rate:     UC.newInput(LANG.cc_plng_s, {title:LANG.cc_plng_l, convert:UC.toInt, units:true}),
         dwell:    UC.newInput(LANG.cd_dwll_s, {title:LANG.cd_dwll_l, convert:UC.toFloat, show:() => poppedRec.axis !== '-'}),
-        lift:     UC.newInput(LANG.cd_lift_s, {title:LANG.cd_lift_l, convert:UC.toFloat, units:true, show:() => poppedRec.axis !== '-'})
+        lift:     UC.newInput(LANG.cd_lift_s, {title:LANG.cd_lift_l, convert:UC.toFloat, units:true, show:() => poppedRec.axis !== '-'}),
+        sep:      UC.newBlank({class:"pop-sep"}),
+        thru:     UC.newInput(LANG.cd_thru_s, {title:LANG.cd_thru_l, convert:UC.toFloat, units:true}),
     };
 
     createPopOp('flip', {
diff --git a/src/kiri-mode/cam/ops.js b/src/kiri-mode/cam/ops.js
index ce823143..55175011 100644
--- a/src/kiri-mode/cam/ops.js
+++ b/src/kiri-mode/cam/ops.js
@@ -1183,7 +1183,7 @@ class OpRegister extends CamOp {
             o3 = tool.fluteDiameter() * 2,
             mx = (lx + hx) / 2,
             my = (ly + hy) / 2,
-            mz = zThru || 0,
+            mz = op.thru || zThru || 0,
             dx = (stock.x - (hx - lx)) / 4,
             dy = (stock.y - (hy - ly)) / 4,
             dz = stock.z,
diff --git a/src/kiri-mode/cam/slice.js b/src/kiri-mode/cam/slice.js
index 67f498eb..f1c4185e 100644
--- a/src/kiri-mode/cam/slice.js
+++ b/src/kiri-mode/cam/slice.js
@@ -40,7 +40,7 @@ CAM.slice = function(settings, widget, onupdate, ondone) {
         zBottom = proc.camZBottom - zbOff,
         zMin = Math.max(bounds.min.z, zBottom),
         zMax = bounds.max.z,
-        zThru = zBottom === 0 ? (proc.camZThru || 0) : 0,
+        zThru = proc.camZBottom ? 0 : (proc.camZThru || 0),
         zTop = zMax + ztOff,
         minToolDiam = Infinity,
         maxToolDiam = -Infinity,
diff --git a/src/kiri/conf.js b/src/kiri/conf.js
index a29ad62f..9b388362 100644
--- a/src/kiri/conf.js
+++ b/src/kiri/conf.js
@@ -518,6 +518,7 @@ const conf = exports({
                 camDrillMark: false,
                 camDrillingOn: false,
                 camRegisterSpeed: 1000,
+                camRegisterThru: 5,
                 camFlipAxis: "X",
                 camFlipOther: "",
                 // camDrillReg: "none",
diff --git a/web/kiri/lang/en.js b/web/kiri/lang/en.js
index 69d03d2a..84508a9a 100644
--- a/web/kiri/lang/en.js
+++ b/web/kiri/lang/en.js
@@ -527,6 +527,8 @@ self.kiri.lang['en-us'] = {
     cd_lift_l:      ["lift between plunges","after dwell period","in workspace units","0 to disable"],
     cd_regi_s:      "register",
     cd_regi_l:      ["drill registration holes","for double-sided parts","independent of enable","drilling but uses same","tool and settings"],
+    cd_thru_s:      "z extend",
+    cd_thru_l:      ["extend downward cut through stock","in workspace units"],
     cd_mark_s:      "marking",
     cd_mark_l:      ["only mark holes, do not drill out","the step down setting is used","to determine how deep to mark"],