RMR is the more common footprint, shared by open-emitter sights like the 507C, 508T, and 507COMP, and it mounts to the widest range of optics-ready pistol slides without an adapter. The K footprint is Holosun's own design, built for compact enclosed sights like the EPS and EPS Carry, and it is closely based on the Shield RMSc pattern. The two footprints are not identical, so K-footprint optics typically ship with an adapter plate rather than mounting directly on an RMSc or RMR cut.

An optics-ready pistol slide has a milled cut in a specific footprint pattern, most commonly RMR or a compact pattern like RMSc. Most Holosun sights list their footprint directly in the specs, and several models, including the EPS and EPS Carry, include an adapter plate to bridge to a different footprint. Footprint information for a specific pistol model is available on that manufacturer's optics-ready specification sheet.

MRS allows switching between reticle options on the same sight: a 2 MOA dot, a wider circle, or a circle-dot combination. The exact circle size depends on the model. The EPS's MRS pairs a 2 MOA dot with a 32 MOA circle. The 507COMP uses its own Performance Reticle System, which pairs a 2 MOA dot with a choice of 8, 20, or 32 MOA circle options. Reticle selection is controlled by the sight's buttons.

MRS (Multi-Reticle System) offers a 2 MOA dot, a 32 MOA circle, or a circle-dot combination, and is used across most of the Holosun lineup, including the EPS, EPS Carry, 507C, and AEMS families. PRS (Performance Reticle System) is used specifically on competition-focused, RMR-footprint optics like the 507COMP and 507-PROMAX, and offers a 2 MOA dot paired with a choice of 8, 20, or 32 MOA circle sizes rather than the single 32 MOA option on MRS. Both are selected using the sight's buttons.

Solar Failsafe adds a solar panel to the sight that supplements the battery and automatically adjusts reticle brightness based on ambient light. Shake Awake powers the sight down while it is stationary and illuminates the reticle when it detects motion. Not every model includes both features: on the EPS, Solar Failsafe is included only on the Multi-Reticle System version, not on the fixed 2 MOA or 6 MOA dot versions.

The EPS is built for full-size carry, duty, and range use: it is fully enclosed to keep dust and moisture off the emitter, has a low deck height for co-witnessing with iron sights, and is available with either the Multi-Reticle System or a fixed 2 MOA or 6 MOA dot. The 507COMP is built for competition: it uses an open-emitter design with a larger 1.1 x 0.87 inch window and the Performance Reticle System, offering three circle-size options around a 2 MOA dot. The EPS mounts on the K footprint; the 507COMP mounts on the RMR footprint.

Pistols are commonly described as full-size, compact, subcompact, or micro-compact based on their overall dimensions, but pistol size does not determine the optic footprint. The exact footprint depends on the firearm's slide cut or factory adapter plate. RMR is common on larger optics-ready pistols, while RMSc and Holosun K-pattern cuts are common on slimline and micro-compact pistols. However, compatibility varies by firearm, and even pistols of the same size can use different footprints. A Glock 19, for example, is a compact pistol that may accept an RMR-footprint Holosun optic like the 507C depending on its exact slide cut, and may require an adapter plate. Always verify the exact optic cut on the specific handgun before purchasing an optic.

Many EDC and concealed-carry pistols use compact footprints such as RMSc or Holosun K, although the exact mounting pattern varies by handgun. The EPS Carry is Holosun's enclosed sight built for slim, compact carry pistols, narrower than the full-size EPS, with an included RMSc-to-K adapter plate. Compact open-emitter options in the same category include the 407K and 507K.

Both are enclosed rifle red dot lines from Holosun, but they use different housing designs. AEMS optics have a rectangular window, ranging from about 1.1 x 0.87 inches on the AEMS-CORE and AEMS-PRO up to 1.58 x 1.18 inches on the AEMS-MAX. ARO optics use a round window sized in millimeters instead, similar to an Aimpoint Micro-style form factor, ranging from 22mm on the ARO-CORE to 26mm on the ARO-EVO. Within each line, the entry-level CORE tier does not include Solar Failsafe, while the EVO tier adds it alongside Shake Awake. Both lines also offer an EVO-DUAL variant that integrates a visible and infrared laser into the sight body.

The number indicates the reticle system: 407-series sights use a single fixed dot, while 507-series sights include the Multi-Reticle System, with a 2 MOA dot, a 32 MOA circle, or a circle-dot combination. The letter indicates the body and footprint rather than the reticle: C-series sights are open-emitter bodies built on the RMR footprint, while K-series sights are the smaller body built for the Holosun K footprint. That means a 407C and 507C share the same body and footprint but differ in reticle, while a 407C and 407K share the same reticle but differ in body and footprint. Generation suffixes like X2 and X3 mark hardware revisions, such as battery tray placement, button size, and housing material, rather than changes to what the number or letter means.