Pentax's constant f/2.8 standard zoom — same family as ID 884, SDM motor version.
The Pentax DA 16-50mm f/2.8 ED AL SDM appears to be a variant of the DA 16-50mm f/2.8 family (ID 884) — with SDM (Supersonic Drive Motor) in the lens rather than body-driven AF. Check for version distinction.
Same constant f/2.8 specification as the SMC version — covering 24-76.5mm equivalent on APS-C. The SDM motor provides in-lens AF — quieter and sometimes faster than body-driven alternatives. ED and AL glass elements.
Pentax K mount with 77mm filter thread. SDM motor — in-lens AF. ED and AL glass. Constant f/2.8. The SDM version preceded the HD DA* 16-50mm f/2.8 PLM AW update.
Check against ID 884 and 996 for version variants. The SDM motor had reliability issues on some Pentax lenses — check AF operation. Available used at mid-range prices. See earlier entries for the complete 16-50mm f/2.8 family details.