Summary for : (1686) De Sitter
C = 1.3 ± 0.6, B = 2.4 ± 0.5, S = 2.7 ± 0.5, M = 3.5 ± 1.0, P = 2.8 ± 1.6, X = 1.9 ± 0.8, Xc = 4.9 ± 0.9, Xk = 4.2 ± 0.7 (Ref) 
Additional resources:
3D Model 
JPL New Horizons 
Minor Planet Center 
Wikipedia (these autogenerated links might not work) Note: The density estimates have been ranked from (A) to (E), corresponding to the relative error: (B) less than 20%, (C) between 20 and 50%, (D) between 50 and 100%, and (E) more than 100%. (A) stands for (presumably) reliable estimates (accuracy better than 20%), based on more than 5 mass estimates and 5 diameter estimates, or a spacecraft encounter. Apparently unrealistic densities (ρ > 8) are tagged with (X). EVM: average by using the Expected Value Method (Ref). w.avg: weighted average (with w = 1/err^2). T.T: Tholen Tax Class. T.B: Bus & Binzel Tax Class. T T.L: S3OS2 Lazarro (Tholen) Tax Class. T.L B: S3OS2 Lazarro (Bus & Binzel) Tax Class. T.D: DeMeo Tax Class. Ref: S = SiMDA, C = Carry (2012) 
Diameter estimatesNotes (N):1: This estimate is discarded for the average diameter (and derived density) calculation in Carry (2012). 2: This estimate is discarded for the average diameter (and derived density) calculation in SiMDA (catalog). NEATM : NearEarth Asteroid Thermal Model. STM : Standard Thermal Model. 
EVM diam. average D = (31.1 ± 1.60) km (ΔD/D = 5%, SNR = 19.44) Derived bulk density ρ = (430.61 ± 213.19) g/cm^{3} (Δρ/ρ = 50%, SNR = 2.0) 
References
