Good question! There are two most common Ruger grip frame and grip sizes: the old model markings for those are XR3 and XR3-RED for the slightly larger size. So those are still referred to when speaking of the new model versions of these two sizes which have different trigger spring attachments and several different markings depending on if they are steel, alloy, or stainless. Your grip number is the new model marking for the XR3-RED size.
All GRIP FRAME MATERIAL & IDENTIFICATION NUMBERS (Founder's Marks) CAST ON GRIP FRAMES (N/A to Bearcat) that I put together.
Notes:
Most all grip frames are 1/2" thick unless otherwise noted below.
For convenience, NM frames in the two most common sizes are often referred to by their old model #s as XR3 'SIZE' or XR3-RED 'SIZE' but they have their own Casting numbers.
NM BLUE: STEEL and ALLOY GFs:
Small steel (OM #XR3 size) 1/8" closer to trigger guard than XR3-RED size, (cut for indexing pawl system, no extensions into main frame & only 7/16" thick) = A (in a square), no other marking observed; w & w/o lock. New Vaq w/o lock has a 512 prefix serial #, locks discontinued in 2012
Large steel (OM #XR3-RED size): Early = A (in a square) XR-3 (that's XR dash 3), Late = A in circle XR-3 1 in circle
Large alloy (OM #XR3-RED size) w/o lock: Early = NXR3-RED, Late = XRN-3RED. With lock = XR & L, locks discontinued in 2012
Short steel 'Vaquerito' .32s (3/16" shorter in length than the XR3 and XR3-RED sizes) = A (in a square) XR-3. If ordered as a separate part = 302 A (in a square)
SBH = No marking on Dragoon frames (1/4" longer than standard grip). Large round guard steel frames supplied on all barrel lengths less than 7 ½" (Old Model #XR3-RED size) = same as Large steel above marking
Birdshead** steel = # in circle, MR00307, A in circle
Bisley** steel grip frames come in only one size that fit all Ruger new models.
NM STAINLESS GFs:
Small, (XR3 size) 1/8" shorter horizontally behind the trigger guard (cut for indexing pawl system, no extensions into main frame & only 7/16" thick = K (in circle); w & w/o lock
Large (OM #XR3-RED size): Earliest = KXR-3*, Next = KXR-3 with a separate N, Late = K (in circle) XRN-3, most current = no markings
Short 'Vaquerito' .32s (3/16" shorter in length than the XR3 and XR3-RED sizes) = KXR-3* and K in circle 302 T in circle
SBH Hunter = KHRN 3 (Dragoon length but with a round trigger guard)
SBH = No marking on Dragoon frames (1/4" longer than standard grip). Large round guard steel frames supplied on all barrel lengths less than 7 ½" (Old Model #XR3-RED size) = same as Large above marking
Birdshead** = # K in circle, MR00307
Bisley** steel grip frames come in only one size that fit all Ruger new models.
OM BLUE STEEL and ALLOY:
Small alloy = XR3, original style to 1962, 1/8" closer to trigger guard than large size
Large alloy = XR3-RED, (part # SS3), new style in 1962 to 1972, also used on Pre 1985 Old Army - alloy w/narrow trig slot, and on Hawkeye - alloy w/wide trigger slot
SBH = steel dragoon, sq back trigger guard (1/4" longer than standard grip) no marking; Early 'long frame' 5/32" longer than later dragoon marked with C (only ~300 made)
Old Army steel (OM XR3-RED size) = XRN-3 beginning 1985 with wide trigger slot and is the only OM GF in carbon steel other than the SBH.
STAINLESS OM - Old Army only:
Large (OM XR3-RED size) = KXR-3*
*Note: same # KXR-3 used on two different frames: earliest NM SS XR3-RED size and OM SS Old Army XR3-RED size, because based on how they are machined, they can be used for either application.
**Birdsheads and Bisleys supplied on New Vaqueros cut for free spin pawl system and have no extensions into main frame, but are interchangeable to all models.
BRASS FRAMES OM only:
Marked "MR-3DB." = Super Blackhawk Brass "Dragoon" style with square back trigger guard. Same dimensions as 1959 Super Blackhawk. Initially for Super Blackhawks only, then shipped on various Blackhawks, majority in 1972.